feat(tier4): Complete GUI integration for patch modal

- Add patch modal state to AppController instead of App
- Add show_patch_modal/hide_patch_modal action handlers
- Fix push_event to work with flat payload format
- Add patch fields to _gettable_fields
- Both GUI integration tests passing

src/gui_2.py

@@ -114,11 +114,6 @@ class App:
   self._tool_log_dirty: bool = True
   self._last_ui_focus_agent: Optional[str] = None
   self._log_registry: Optional[log_registry.LogRegistry] = None
-  # Patch viewer state for Tier 4 auto-patching
-  self._pending_patch_text: Optional[str] = None
-  self._pending_patch_files: list[str] = []
-  self._show_patch_modal: bool = False
-  self._patch_error_message: Optional[str] = None
 
  def _handle_approve_tool(self, user_data=None) -> None:
   """UI-level wrapper for approving a pending tool execution ask."""