refactor(ai): use stateful autocomplete for provider name matching

Replace the manual GHashTable iteration in ai_providers_find() with the
existing stateful autocomplete system. Provider names are now kept in
sync via autocomplete_add/remove during ai_add_provider/ai_remove_provider,
and ai_providers_find delegates to autocomplete_complete() for deterministic
tab-completion cycling through sorted results.

This eliminates manual GList allocation, iteration, and cleanup, while
providing consistent forward/backward cycling behavior shared by all
autocomplete callers.

src/ai/ai_client.c

@@ -15,6 +15,7 @@
 #include "log.h"
 #include "config/preferences.h"
 #include "profanity.h"
+#include "tools/autocomplete.h"
 #include "ui/ui.h"
 
 #include <curl/curl.h>
@@ -28,6 +29,7 @@
 /* Global state */
 static GHashTable* providers = NULL;
 static GHashTable* provider_keys = NULL;
+static Autocomplete providers_ac = NULL;
 
 /* ========================================================================
  * Curl helpers
@@ -245,6 +247,9 @@ ai_client_init(void)
     providers = g_hash_table_new_full(g_str_hash, g_str_equal, g_free, (GDestroyNotify)ai_provider_unref);
     provider_keys = g_hash_table_new_full(g_str_hash, g_str_equal, g_free, g_free);
 
+    /* Create autocomplete for provider names */
+    providers_ac = autocomplete_new();
+
     /* Add default providers */
     ai_add_provider("openai", DEFAULT_OPENAI_URL, NULL);
     ai_add_provider("perplexity", DEFAULT_PERPLEXITY_URL, NULL);
@@ -266,6 +271,11 @@ ai_client_shutdown(void)
     providers = NULL;
     provider_keys = NULL;
 
+    if (providers_ac) {
+        autocomplete_free(providers_ac);
+        providers_ac = NULL;
+    }
+
     curl_global_cleanup();
     log_info("AI client shutdown");
 }
@@ -304,6 +314,9 @@ ai_add_provider(const gchar* name, const gchar* api_url, const gchar* org_id)
     AIProvider* provider = ai_provider_new(name, api_url, org_id);
     g_hash_table_insert(providers, g_strdup(name), provider);
 
+    /* Sync autocomplete */
+    autocomplete_add(providers_ac, name);
+
     log_info("Added provider: %s (URL: %s)", name, api_url);
     return provider; /* Caller gets non-owning pointer; hash table owns ref */
 }
@@ -313,6 +326,10 @@ ai_remove_provider(const gchar* name)
 {
     if (!name || !providers)
         return FALSE;
+
+    /* Sync autocomplete before removing */
+    autocomplete_remove(providers_ac, name);
+
     return g_hash_table_remove(providers, name);
 }
 
@@ -334,40 +351,23 @@ ai_list_providers(void)
     return result;
 }
 
+/* ========================================================================
+ * Provider autocomplete state
+ * ======================================================================== */
+
+/* Stateful provider name finder with case-sensitive matching.
+ * Maintains position in sorted list for deterministic tab-completion cycling.
+ * The autocomplete is kept in sync via ai_add_provider/ai_remove_provider. */
 char*
 ai_providers_find(const char* const search_str, gboolean previous, void* context)
 {
-    if (!providers || !search_str || strlen(search_str) == 0) {
-        return NULL;
+    /* Initialize autocomplete on first use */
+    if (!providers_ac) {
+        providers_ac = autocomplete_new();
     }
 
-    GHashTableIter iter;
-    gpointer key;
-    gpointer value;
-
-    /* Collect all matching providers */
-    GList* matches = NULL;
-    g_hash_table_iter_init(&iter, providers);
-    while (g_hash_table_iter_next(&iter, &key, &value)) {
-        if (g_str_has_prefix((gchar*)key, search_str)) {
-            matches = g_list_append(matches, g_strdup((gchar*)key));
-        }
-    }
-
-    if (matches == NULL) {
-        return NULL;
-    }
-
-    /* Return first or last match based on previous flag */
-    gchar* result;
-    if (previous) {
-        result = g_strdup((gchar*)matches->data);
-    } else {
-        result = g_strdup((gchar*)g_list_last(matches)->data);
-    }
-
-    g_list_free_full(matches, g_free);
-    return result;
+    /* Use stateful autocomplete */
+    return autocomplete_complete(providers_ac, search_str, FALSE, previous);
 }
 
 gchar*