fix(ai): add reset for models_ac and streamline model autocomplete handling

Replace the custom ai_models_find function with a dedicated
ai_models_ac autocomplete list. Update the /ai switch trigger to
include a trailing space for consistent parsing.

src/ai/ai_client.c

@@ -406,37 +406,6 @@ ai_providers_find(const char* const search_str, gboolean previous, void* context
     return autocomplete_complete(providers_ac, search_str, FALSE, previous);
 }
 
-/* Stateful model name finder for autocomplete.
- * Uses the current session's provider models for completion. */
-gchar*
-ai_models_find(const char* const search_str, gboolean previous, void* context)
-{
-    ProfAiWin* aiwin = (ProfAiWin*)context;
-    if (!aiwin || !aiwin->session) {
-        return NULL;
-    }
-
-    AIProvider* provider = aiwin->session->provider;
-    if (!provider || !provider->models) {
-        return NULL;
-    }
-
-    /* Create a temporary autocomplete for models */
-    Autocomplete models_ac = autocomplete_new();
-    GList* curr = provider->models;
-    while (curr) {
-        autocomplete_add(models_ac, curr->data);
-        curr = g_list_next(curr);
-    }
-
-    /* NULL search_str is treated as empty string for cycling */
-    const char* effective_search = (search_str != NULL) ? search_str : "";
-
-    gchar* result = autocomplete_complete(models_ac, effective_search, FALSE, previous);
-    autocomplete_free(models_ac);
-    return result;
-}
-
 /* Reset the provider autocomplete state.
  * Called from cmd_ac_reset() to clear autocomplete state when the user presses Ctrl+C. */
 void