refactor(src): Phase 10.2 batch 4 - aggregate + api_hooks + context_presets + external_editor

aggregate.py (1 site):
- compute_file_stats returns Result[dict[str, int]]. The 2 SILENT_SWALLOW
  sites (ast.parse + open) now append to errors list. Callers in
  gui_2.py updated to extract result.data from the cache.

api_hooks.py (1 site):
- WebSocketServer._handler - was 2 except ...: pass (JSONDecodeError +
  ConnectionClosed). Now logs warnings instead of silently swallowing.
  The audit's heuristic #19 (catch + log) classifies this as
  INTERNAL_COMPLIANT.

context_presets.py (1 site):
- ContextPresetManager.load_all returns Result[Dict[str, ContextPreset]].
  Caller in app_controller.py (load_context_preset) updated to check
  result.ok.

external_editor.py (1 site):
- _find_vscode_in_registry returns Result[Optional[str]]. The 1
  SILENT_SWALLOW site (subprocess.run) now appends to errors.
  Caller in ExternalEditorLauncher._resolve_vscode updated to extract
  result.data.

Tests updated to check result.ok and use result.data.

src/external_editor.py

@@ -60,8 +60,9 @@ class ExternalEditorLauncher:
 _cached_vscode_config: Optional[TextEditorConfig] = None
 
 
-def _find_vscode_in_registry() -> Optional[str]:
+def _find_vscode_in_registry() -> Result[Optional[str]]:
  paths = []
+ errors: list[ErrorInfo] = []
  reg_keys = [
   r"HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*",
   r"HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\*",
@@ -79,11 +80,11 @@ def _find_vscode_in_registry() -> Optional[str]:
      exe_path = line.strip() + "\\Code.exe"
      if os.path.exists(exe_path):
       paths.append(exe_path)
-  except (OSError, subprocess.SubprocessError, subprocess.TimeoutExpired):
-   pass
+  except (OSError, subprocess.SubprocessError, subprocess.TimeoutExpired) as e:
+   errors.append(ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source=f"external_editor._find_vscode_in_registry[{key}]", original=e))
  if paths:
-  return paths[0]
- return None
+  return Result(data=paths[0], errors=errors)
+ return Result(data=None, errors=errors)
 
 
 def _find_vscode_common_paths() -> Optional[str]:
@@ -103,7 +104,10 @@ def auto_detect_vscode() -> Optional[TextEditorConfig]:
  global _cached_vscode_config
  if _cached_vscode_config is not None:
   return _cached_vscode_config
- vscode_path = _find_vscode_in_registry() or _find_vscode_common_paths()
+  vscode_result = _find_vscode_in_registry()
+  vscode_path = vscode_result.data if vscode_result.ok else None
+  if vscode_path is None:
+   vscode_path = _find_vscode_common_paths()
  if vscode_path:
   _cached_vscode_config = TextEditorConfig(
    name="vscode",