ref(ai): remove org_id from provider configuration

The org_id field was removed from AIProvider as it was no longer
populated through the command surface. The /ai set org command was
previously removed, leaving org_id as dead code.

This change removes org_id from:
- AIProvider struct definition
- ai_provider_new() and ai_provider_unref()
- ai_add_provider() API signature
- _build_curl_headers() (OpenAI-Organization header)
- cmd_ai_set() and cmd_ai_providers()
- All unit tests

src/command/cmd_funcs.c

@@ -10839,7 +10839,7 @@ cmd_ai_set(ProfWin* window, const char* const command, gchar** args)
             cons_bad_cmd_usage(command);
             return TRUE;
         }
-        if (ai_add_provider(args[2], args[3], NULL)) {
+        if (ai_add_provider(args[2], args[3])) {
             cons_show("Provider '%s' configured with URL: %s", args[2], args[3]);
         } else {
             cons_show_error("Failed to configure provider '%s'.", args[2]);
@@ -11218,9 +11218,6 @@ cmd_ai_providers(ProfWin* window, const char* const command, gchar** args)
         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);
     }