fix(ai): fix memory leaks in ai session handling

Add missing `ai_session_unref` calls to prevent memory leaks.

- In `_ai_request_thread`, release session on error paths and
  after successful processing.
- In `cmd_ai_start`, release reference after passing ownership
  to the AI window.

src/ai/ai_client.c

@@ -1434,6 +1434,7 @@ _ai_request_thread(gpointer data)
                                                       local_provider_name, local_provider_name);
         log_error("AI request failed for %s/%s: %s", local_provider_name, local_model, error_msg);
         _aiwin_display_error(user_data, error_msg);
+        ai_session_unref(session);
         g_free(args);
         return NULL;
     }
@@ -1444,6 +1445,7 @@ _ai_request_thread(gpointer data)
         log_error("AI request failed for %s/%s: Failed to initialize curl",
                   local_provider_name, local_model);
         _aiwin_display_error(user_data, "Failed to initialize curl.");
+        ai_session_unref(session);
         g_free(args);
         return NULL;
     }
@@ -1531,6 +1533,7 @@ _ai_request_thread(gpointer data)
 
     ai_provider_unref(local_provider);
 
+    ai_session_unref(session);
     g_free(args);
 
     return NULL;

src/command/cmd_funcs.c

@@ -10981,6 +10981,9 @@ cmd_ai_start(ProfWin* window, const char* const command, gchar** args)
     }
     log_debug("[AI-CMD] wins_new_ai() returned successfully, window type: %d", ai_win->type);
 
+    // Release the reference held by cmd_ai_start, since the window now holds one
+    ai_session_unref(session);
+
     // 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);