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/context_presets.py

@@ -1,22 +1,23 @@
 from typing import Dict, Any
 
 from src.models import ContextPreset
+from src.result_types import Result, ErrorInfo, ErrorKind
 
 
 class ContextPresetManager:
  """Manages context presets within the project dictionary (manual_slop.toml)."""
 
- def load_all(self, project_dict: Dict[str, Any]) -> Dict[str, ContextPreset]:
+ def load_all(self, project_dict: Dict[str, Any]) -> Result[Dict[str, ContextPreset]]:
   """Loads all context presets from the project dictionary."""
   presets: Dict[str, ContextPreset] = {}
+  errors: list[ErrorInfo] = []
   presets_data = project_dict.get("context_presets", {})
   for name, data in presets_data.items():
    try:
     presets[name] = ContextPreset.from_dict(name, data)
-   except (ValueError, KeyError, TypeError):
-    # Silent failure or logging could be added here
-    pass
-  return presets
+   except (ValueError, KeyError, TypeError) as e:
+    errors.append(ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source=f"context_presets.load_all[{name}]", original=e))
+  return Result(data=presets, errors=errors)
 
  def save_preset(self, project_dict: Dict[str, Any], preset: ContextPreset) -> None:
   """Saves a context preset into the project dictionary."""