feat(ai): add AI client with multi-provider support and UI

Add an AI client module that integrates with OpenAI-compatible API
providers (OpenAI, Perplexity, and custom providers) to provide
AI-assisted responses within the profanity client.

The implementation includes:

- src/ai/ai_client.c/h: Core AI client with provider management,
  session handling, and async HTTP request handling via libcurl.
  Supports per-provider API keys stored in preferences, reference-
  counted sessions, and conversation history tracking.

- src/ui/window.c/window_list.c: New AI window type (ProfAiWin) for
  displaying AI conversations, with response streaming and error
  display capabilities.

- Command integration: New `/ai` command (cmd_defs.c, cmd_funcs.c)
  for creating sessions, sending prompts, and managing providers.
  Provider autocomplete support in cmd_ac.c.

- Preferences integration: API keys for providers are persisted in
  the preferences system (config/preferences.c).

- Unit tests: 472 lines of comprehensive tests covering provider
  management, session lifecycle, JSON escaping, and autocomplete
  (tests/unittests/test_ai_client.c).

Architecture decisions:
- Asynchronous design: HTTP requests run on a separate thread to
  avoid blocking the main UI loop. Callbacks are invoked on the main
  thread via direct function call (profanity uses ncurses, not GLib
  main loop).
- Reference counting: Both AIProvider and AISession use ref counting
  for safe shared ownership.
- Response size limit: 10MB cap on HTTP responses to prevent OOM.

src/command/cmd_funcs.c

@@ -117,6 +117,8 @@
 #include "tools/clipboard.h"
 #endif
 
+#include "ai/ai_client.h"
+
 #ifdef HAVE_PYTHON
 #include "plugins/python_plugins.h"
 #endif
@@ -8326,7 +8328,7 @@ _cmd_execute_default(ProfWin* window, const char* inp)
     }
 
     // handle non commands in non chat or plugin windows
-    if (window->type != WIN_CHAT && window->type != WIN_MUC && window->type != WIN_PRIVATE && window->type != WIN_PLUGIN && window->type != WIN_XML) {
+    if (window->type != WIN_CHAT && window->type != WIN_MUC && window->type != WIN_PRIVATE && window->type != WIN_PLUGIN && window->type != WIN_XML && window->type != WIN_AI) {
         cons_show("Unknown command: %s", inp);
         cons_alert(NULL);
         return TRUE;
@@ -8372,6 +8374,13 @@ _cmd_execute_default(ProfWin* window, const char* inp)
         connection_send_stanza(inp);
         break;
     }
+    case WIN_AI:
+    {
+        ProfAiWin* aiwin = (ProfAiWin*)window;
+        assert(aiwin->memcheck == PROFAIWIN_MEMCHECK);
+        aiwin_send_message(aiwin, inp, NULL);
+        break;
+    }
     default:
         break;
     }
@@ -10640,6 +10649,298 @@ cmd_vcard_save(ProfWin* window, const char* const command, gchar** args)
     return TRUE;
 }
 
+gboolean
+cmd_ai(ProfWin* window, const char* const command, gchar** args)
+{
+    if (args[0] == NULL) {
+        // Display current AI settings
+        cons_show("AI Chat - OpenAI-compatible API client");
+        cons_show("");
+
+        // List available providers
+        GList* providers = ai_list_providers();
+        cons_show("Available providers:");
+        for (GList* curr = providers; curr; curr = g_list_next(curr)) {
+            AIProvider* provider = curr->data;
+            const gchar* key = ai_get_provider_key(provider->name);
+            cons_show("  %s (URL: %s, Key: %s)",
+                      provider->name,
+                      provider->api_url,
+                      key ? "set" : "not set");
+        }
+        g_list_free(providers);
+
+        cons_show("");
+        cons_show("Use '/ai start <provider>/<model>' to begin a chat.");
+        cons_show("Available models: https://models.litellm.ai/");
+        return TRUE;
+    }
+
+    cons_bad_cmd_usage(command);
+    return TRUE;
+}
+
+gboolean
+cmd_ai_set(ProfWin* window, const char* const command, gchar** args)
+{
+    if (args[1] == NULL) {
+        cons_bad_cmd_usage(command);
+        return TRUE;
+    }
+
+    if (g_strcmp0(args[1], "provider") == 0) {
+        // /ai set provider <name> <url>
+        if (g_strv_length(args) < 4) {
+            cons_bad_cmd_usage(command);
+            return TRUE;
+        }
+        if (ai_add_provider(args[2], args[3], NULL)) {
+            cons_show("Provider '%s' configured with URL: %s", args[2], args[3]);
+        } else {
+            cons_show_error("Failed to configure provider '%s'.", args[2]);
+        }
+        cons_show("");
+        return TRUE;
+    } else if (g_strcmp0(args[1], "token") == 0) {
+        // /ai set token <provider> <token>
+        if (g_strv_length(args) < 4) {
+            cons_bad_cmd_usage(command);
+            return TRUE;
+        }
+        ai_set_provider_key(args[2], args[3]);
+        cons_show("API token set for provider: %s", args[2]);
+        cons_show("");
+        return TRUE;
+    } else if (g_strcmp0(args[1], "org") == 0) {
+        // /ai set org <provider> <org_id>
+        if (g_strv_length(args) < 4) {
+            cons_bad_cmd_usage(command);
+            return TRUE;
+        }
+        AIProvider* provider = ai_get_provider(args[2]);
+        if (provider) {
+            g_free(provider->org_id);
+            provider->org_id = g_strdup(args[3]);
+            cons_show("Organization ID set for provider: %s", args[2]);
+        } else {
+            cons_show("Provider '%s' not found. Add it first with '/ai set provider'.", args[2]);
+        }
+        cons_show("");
+        return TRUE;
+    }
+
+    cons_bad_cmd_usage(command);
+    return TRUE;
+}
+
+gboolean
+cmd_ai_remove(ProfWin* window, const char* const command, gchar** args)
+{
+    // /ai remove provider <name>
+    if (g_strcmp0(args[1], "provider") != 0) {
+        cons_bad_cmd_usage(command);
+        return TRUE;
+    }
+
+    if (g_strv_length(args) < 3) {
+        cons_bad_cmd_usage(command);
+        return TRUE;
+    }
+
+    if (ai_remove_provider(args[2])) {
+        cons_show("Provider '%s' removed.", args[2]);
+    } else {
+        cons_show("Provider '%s' not found.", args[2]);
+    }
+    cons_show("");
+    return TRUE;
+}
+
+gboolean
+cmd_ai_start(ProfWin* window, const char* const command, gchar** args)
+{
+    // /ai start [<provider>/<model>]
+    const gchar* provider_model = (g_strv_length(args) >= 2) ? args[1] : NULL;
+
+    const gchar* provider_name = "openai";
+    const gchar* model = "gpt-4o";
+
+    if (provider_model) {
+        const gchar* slash = strchr(provider_model, '/');
+        if (slash) {
+            provider_name = g_strndup(provider_model, slash - provider_model);
+            model = slash + 1;
+        } else {
+            // Just a model name, use default provider
+            model = provider_model;
+        }
+    }
+
+    // Check if provider exists
+    AIProvider* provider = ai_get_provider(provider_name);
+    if (!provider) {
+        cons_show_error("Provider '%s' not found. Use '/ai set provider %s <url>' to add it.",
+                        provider_name, provider_name);
+        return TRUE;
+    }
+
+    // Check for API key
+    gchar* api_key = ai_get_provider_key(provider_name);
+    if (!api_key || strlen(api_key) == 0) {
+        cons_show_error("No API key set for provider '%s'. Use '/ai set token %s <key>' first.",
+                        provider_name, provider_name);
+        g_free(api_key);
+        return TRUE;
+    }
+    g_free(api_key);
+
+    // Create new AI session
+    AISession* session = ai_session_create(provider_name, model);
+    if (!session) {
+        log_error("[AI-CMD] Failed to create AI session");
+        cons_show_error("Failed to create AI session for %s/%s.", provider_name, model);
+        return TRUE;
+    }
+    log_debug("[AI-CMD] AI session created successfully");
+
+    // Create AI chat window
+    log_debug("[AI-CMD] Calling wins_new_ai()...");
+    ProfWin* ai_win = wins_new_ai(session);
+    if (!ai_win) {
+        log_error("[AI-CMD] wins_new_ai() returned NULL");
+        cons_show_error("Failed to create AI chat window.");
+        ai_session_unref(session);
+        return TRUE;
+    }
+    log_debug("[AI-CMD] wins_new_ai() returned successfully, window type: %d", ai_win->type);
+
+    // Add welcome message to the AI window
+    log_debug("[AI-CMD] Adding welcome messages...");
+    win_println(ai_win, THEME_DEFAULT, "-", "AI Chat: %s/%s", provider_name, model);
+    win_println(ai_win, THEME_DEFAULT, "-", "Type your message and press Enter to start a conversation.");
+    log_debug("[AI-CMD] Welcome messages added");
+
+    // Focus the new window
+    log_debug("[AI-CMD] Calling ui_focus_win()...");
+    ui_focus_win(ai_win);
+    log_debug("[AI-CMD] ui_focus_win() returned");
+
+    cons_show("Started AI chat: %s/%s", provider_name, model);
+    cons_show("");
+    log_debug("[AI-CMD] AI start command completed");
+
+    return TRUE;
+}
+
+gboolean
+cmd_ai_clear(ProfWin* window, const char* const command, gchar** args)
+{
+    // /ai clear
+    ProfAiWin* aiwin = (window && window->type == WIN_AI) ? (ProfAiWin*)window : wins_get_ai();
+
+    if (aiwin) {
+        assert(aiwin->memcheck == PROFAIWIN_MEMCHECK);
+        if (aiwin->session) {
+            ai_session_clear_history(aiwin->session);
+        }
+        cons_show("Chat history cleared.");
+    } else {
+        cons_show("No active AI chat window to clear.");
+    }
+    cons_show("");
+    return TRUE;
+}
+
+gboolean
+cmd_ai_correct(ProfWin* window, const char* const command, gchar** args)
+{
+    // /ai correct <message>
+    if (args[1] == NULL) {
+        cons_bad_cmd_usage(command);
+        return TRUE;
+    }
+
+    // Get current AI window
+    ProfAiWin* aiwin = wins_get_ai();
+    if (!aiwin) {
+        cons_show("No active AI chat window. Use '/ai start <provider>/<model>' first.");
+        return TRUE;
+    }
+
+    assert(aiwin->memcheck == PROFAIWIN_MEMCHECK);
+
+    if (!aiwin->session) {
+        cons_show("No active session in this chat window.");
+        return TRUE;
+    }
+
+    // Get the last user message and replace it
+    GList* history = aiwin->session->history;
+    GList* last_user_msg = NULL;
+    for (GList* curr = history; curr; curr = g_list_next(curr)) {
+        AIMessage* msg = curr->data;
+        if (g_strcmp0(msg->role, "user") == 0) {
+            last_user_msg = curr;
+        }
+    }
+
+    if (!last_user_msg) {
+        cons_show("No user messages in this chat to correct.");
+        return TRUE;
+    }
+
+    // Replace the last user message
+    AIMessage* msg = last_user_msg->data;
+    g_free(msg->content);
+    msg->content = g_strdup(args[1]);
+
+    // Resend the prompt
+    cons_show("Correcting message...");
+    ai_send_prompt(aiwin->session, args[1],
+                   (ai_response_cb)aiwin_display_response,
+                   (ai_error_cb)aiwin_display_error,
+                   aiwin);
+
+    return TRUE;
+}
+
+gboolean
+cmd_ai_providers(ProfWin* window, const char* const command, gchar** args)
+{
+    if (args[1] == NULL || g_strcmp0(args[1], "list") != 0) {
+        // List all available providers
+        cons_show("Available AI providers:");
+        cons_show("");
+        cons_show("  openai      - OpenAI API (https://api.openai.com)");
+        cons_show("  perplexity  - Perplexity API (https://api.perplexity.ai)");
+        cons_show("");
+        cons_show("Add custom providers with: /ai set provider <name> <url>");
+        return TRUE;
+    }
+
+    // List configured providers with key status
+    cons_show("Configured providers:");
+    cons_show("");
+
+    GList* providers = ai_list_providers();
+    for (GList* curr = providers; curr; curr = g_list_next(curr)) {
+        AIProvider* provider = curr->data;
+        gchar* key = ai_get_provider_key(provider->name);
+        cons_show("  %s", provider->name);
+        cons_show("    URL: %s", provider->api_url);
+        cons_show("    Key: %s", key ? "configured" : "NOT configured");
+        if (provider->org_id && strlen(provider->org_id) > 0) {
+            cons_show("    Org: %s", provider->org_id);
+        }
+        cons_show("");
+        g_free(key);
+        ai_provider_unref(provider);
+    }
+    g_list_free(providers);
+
+    return TRUE;
+}
+
 gboolean
 cmd_force_encryption(ProfWin* window, const char* const command, gchar** args)
 {