fix(ai): use atomic ai_provider_ref() in cmd_ai_switch

src/command/cmd_funcs:11118 used a plain non-atomic ref_count++ on
ai_provider, which is a data race against concurrent
ai_provider_unref() calls using g_atomic_int_dec_and_test.

- Expose ai_provider_ref() in ai_client.h (was static)
- Replace non-atomic ref_count++ with ai_provider_ref() in cmd_ai_switch"

src/ai/ai_client.c

@@ -205,7 +205,7 @@ ai_provider_new(const gchar* name, const gchar* api_url, const gchar* org_id)
     return provider;
 }
 
-static AIProvider*
+AIProvider*
 ai_provider_ref(AIProvider* provider)
 {
     if (provider) {

src/ai/ai_client.h

@@ -78,6 +78,13 @@ AIProvider* ai_add_provider(const gchar* name, const gchar* api_url, const gchar
  */
 gboolean ai_remove_provider(const gchar* name);
 
+/**
+ * Increment the reference count of a provider.
+ * @param provider The provider to reference
+ * @return The same provider pointer
+ */
+AIProvider* ai_provider_ref(AIProvider* provider);
+
 /**
  * Decrement the reference count of a provider.
  * @param provider The provider to unreference

src/command/cmd_funcs.c

@@ -11115,7 +11115,7 @@ cmd_ai_switch(ProfWin* window, const char* const command, gchar** args)
         aiwin->session->provider_name = g_strdup(provider_name);
         ai_provider_unref(aiwin->session->provider);
         aiwin->session->provider = new_provider;
-        aiwin->session->provider->ref_count++;
+        ai_provider_ref(aiwin->session->provider);
     }
     g_free(aiwin->session->model);
     aiwin->session->model = g_strdup(model);