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_process_pending_gui_tasks.py

@@ -1,7 +1,7 @@
 from typing import Generator
 import pytest
 from unittest.mock import patch, Mock
-from src import ai_client_stub
+from src import ai_client
 from src.gui_2 import App
 
 @pytest.fixture
@@ -20,8 +20,8 @@ def app_instance() -> Generator[App, None, None]:
   patch('src.app_controller.AppController.start_services'),
   # Do not patch _init_ai_and_hooks to ensure _settable_fields is initialized
   patch('src.api_hooks.HookServer'),
-  patch('src.ai_client_stub.set_provider'),
-  patch('src.ai_client_stub.reset_session')
+  patch('src.ai_client.set_provider'),
+  patch('src.ai_client.reset_session')
  ):
   app = App()
   yield app
@@ -30,8 +30,8 @@ def test_redundant_calls_in_process_pending_gui_tasks(app_instance: App) -> None
  app_instance.controller._pending_gui_tasks = [
   {'action': 'set_value', 'item': 'current_provider', 'value': 'anthropic'}
  ]
- with patch('src.ai_client_stub.set_provider') as mock_set_provider, \
-      patch('src.ai_client_stub.reset_session') as mock_reset_session:
+ with patch('src.ai_client.set_provider') as mock_set_provider, \
+      patch('src.ai_client.reset_session') as mock_reset_session:
   app_instance.controller._process_pending_gui_tasks()
   assert mock_set_provider.call_count == 1
   assert mock_reset_session.call_count == 1
@@ -42,10 +42,10 @@ def test_gcli_path_updates_adapter(app_instance: App) -> None:
   {'action': 'set_value', 'item': 'gcli_path', 'value': '/new/path/to/gemini'}
  ]
  # Initialize adapter if it doesn't exist (it shouldn't in mock env)
- ai_client_stub._gemini_cli_adapter = None
+ ai_client._gemini_cli_adapter = None
  app_instance.controller._process_pending_gui_tasks()
- assert ai_client_stub._gemini_cli_adapter is not None
- assert ai_client_stub._gemini_cli_adapter.binary_path == '/new/path/to/gemini'
+ assert ai_client._gemini_cli_adapter is not None
+ assert ai_client._gemini_cli_adapter.binary_path == '/new/path/to/gemini'
 
 def test_process_pending_gui_tasks_drag(app_instance: App) -> None:
  """Test that the drag action is correctly processed and dispatches to the registered callback."""