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/shell_runner.py

@@ -44,13 +44,14 @@ def _build_subprocess_env() -> dict[str, str]:
   env[key] = os.path.expandvars(str(val))
  return env
 
-def run_powershell(script: str, base_dir: str, qa_callback: Optional[Callable[[str], str]] = None) -> str:
+def run_powershell(script: str, base_dir: str, qa_callback: Optional[Callable[[str], str]] = None, patch_callback: Optional[Callable[[str, str], Optional[str]]] = None) -> str:
  """
     Run a PowerShell script with working directory set to base_dir.
     Returns a string combining stdout, stderr, and exit code.
     Environment is configured via mcp_env.toml (project root).
     If qa_callback is provided and the command fails or has stderr,
     the callback is called with the stderr content and its result is appended.
+    If patch_callback is provided, it receives (error, file_context) and returns patch text.
     """
  safe_dir: str = str(base_dir).replace("'", "''")
  full_script: str = f"Set-Location -LiteralPath '{safe_dir}'\n{script}"
@@ -72,6 +73,10 @@ def run_powershell(script: str, base_dir: str, qa_callback: Optional[Callable[[s
    qa_analysis: Optional[str] = qa_callback(stderr.strip())
    if qa_analysis:
     parts.append(f"\nQA ANALYSIS:\n{qa_analysis}")
+  if patch_callback and (process.returncode != 0 or stderr.strip()):
+   patch_text = patch_callback(stderr.strip(), base_dir)
+   if patch_text:
+    parts.append(f"\nAUTO_PATCH:\n{patch_text}")
   return "\n".join(parts)
  except subprocess.TimeoutExpired:
   if 'process' in locals() and process: