fix(ai): align ai_list_providers with documented contract

Remove ai_provider_ref() from ai_list_providers() so the returned
providers do not need to be unref'd by the caller. This matches the
header docstring which states "caller must not free the list or
providers". Also update all callers (cmd_ai_providers, tests) to
remove redundant ai_provider_unref() calls.

src/ai/ai_client.c

@@ -328,7 +328,7 @@ ai_list_providers(void)
 
     g_hash_table_iter_init(&iter, providers);
     while (g_hash_table_iter_next(&iter, &key, &value)) {
-        result = g_list_append(result, ai_provider_ref((AIProvider*)value));
+        result = g_list_append(result, value);
     }
 
     return result;

src/ai/ai_client.h

@@ -97,7 +97,8 @@ void ai_provider_unref(AIProvider* provider);
 
 /**
  * List all configured providers.
- * @return GList of AIProvider* (caller must not free the list or providers)
+ * @return GList of AIProvider* (caller must not free the list or providers,
+ *         and must not unref the returned providers)
  */
 GList* ai_list_providers(void);
 

src/command/cmd_funcs.c

@@ -10929,7 +10929,6 @@ cmd_ai_providers(ProfWin* window, const char* const command, gchar** args)
         }
         cons_show("");
         g_free(key);
-        ai_provider_unref(provider);
     }
     g_list_free(providers);
 

tests/unittests/test_ai_client.c

@@ -78,10 +78,7 @@ test_ai_list_providers(void** state)
     assert_non_null(providers);
     assert_int_equal(2, g_list_length(providers)); /* openai and perplexity */
 
-    /* Free list and unref providers (ai_list_providers returns ref'd providers) */
-    for (GList* l = providers; l; l = g_list_next(l)) {
-        ai_provider_unref(l->data);
-    }
+    /* Free list (ai_list_providers returns non-ref'd providers; caller must not unref) */
     g_list_free(providers);
 
     /* Add another provider */
@@ -89,10 +86,7 @@ test_ai_list_providers(void** state)
     providers = ai_list_providers();
     assert_int_equal(3, g_list_length(providers));
 
-    /* Free list and unref providers */
-    for (GList* l = providers; l; l = g_list_next(l)) {
-        ai_provider_unref(l->data);
-    }
+    /* Free list */
     g_list_free(providers);
 }