feat(tier4): Integrate patch generation into GUI workflow

- Add patch_callback parameter throughout the tool execution chain
- Add _render_patch_modal() to gui_2.py with colored diff display
- Add patch modal state variables to App.__init__
- Add request_patch_from_tier4() to trigger patch generation
- Add run_tier4_patch_callback() to ai_client.py
- Update shell_runner to accept and execute patch_callback
- Diff colors: green for additions, red for deletions, cyan for headers
- 36 tests passing

src/multi_agent_conductor.py

@@ -410,6 +410,7 @@ def run_worker_lifecycle(ticket: Ticket, context: WorkerContext, context_files:
    base_dir=".",
    pre_tool_callback=clutch_callback if ticket.step_mode else None,
    qa_callback=ai_client.run_tier4_analysis,
+   patch_callback=ai_client.run_tier4_patch_callback,
    stream_callback=stream_callback
   )
  finally: