remove(ai_client): delete unused stub and proxy files

Deleted:
- src/ai_client_stub.py
- src/ai_client_proxy.py

Fixed test imports to use ai_client instead of ai_client_stub.

tests/test_gui_updates.py

@@ -31,7 +31,7 @@ def test_telemetry_data_updates_correctly(app_instance: Any) -> None:
    "percentage": 75.0,
   }
   # 3. Patch the dependencies
-  with patch('src.ai_client_stub.get_token_stats', return_value=mock_stats) as mock_get_stats:
+  with patch('src.ai_client.get_token_stats', return_value=mock_stats) as mock_get_stats:
   # 4. Call the method under test
    app_instance._refresh_api_metrics({}, md_content="test content")
   # 5. Assert the results
@@ -60,7 +60,7 @@ def test_gui_updates_on_event(app_instance: App) -> None:
  """
  mock_stats = {"percentage": 50.0, "current": 500, "limit": 1000}
  app_instance.last_md = "mock_md"
- with patch('src.ai_client_stub.get_token_stats', return_value=mock_stats):
+ with patch('src.ai_client.get_token_stats', return_value=mock_stats):
   # Drain the queue
   while not app_instance.event_queue.empty():
    app_instance.event_queue.get()