refactor(src): migrate src/summary_cache.py to Result[T] error handling (4 sites)

Migrates the 4 try/except sites in SummaryCache:

1. load() - line 39: was `except Exception: self.cache = {}`
   Now `except (OSError, json.JSONDecodeError):` and returns
   Result[bool] with ErrorInfo on failure.

2. save() - line 48: was `except Exception: pass`
   Now `except OSError:` and returns Result[bool] with ErrorInfo on
   failure.

3. clear() - line 91: was `except Exception: pass`
   Now `except OSError:` and returns Result[bool] with ErrorInfo on
   failure.

4. get_stats() - line 100: was `except Exception: pass`
   Now `except OSError:` and returns Result[dict] with default empty
   size_bytes on failure.

All 4 sites narrowed from broad `except Exception` to specific stdlib
I/O exceptions (OSError, json.JSONDecodeError). Methods that previously
returned None now return Result[bool]; get_stats() now returns
Result[dict] instead of dict.

Callers (app_controller.py:_handle_clear_summary_cache, _cb_clear_summary_cache,
summarize.py) ignore the return value, which is backwards-compatible.

Tests verified:
- tests/test_summary_cache.py (3 tests) PASS
- tests/test_ui_cache_controls_sim.py (1 live_gui test) PASS

src/summary_cache.py

@@ -4,6 +4,8 @@ import json
 from pathlib import Path
 from typing  import Optional, Dict
 
+from src.result_types import Result, ErrorInfo, ErrorKind
+
 
 def get_file_hash(content: str) -> str:
  """
@@ -27,26 +29,30 @@ class SummaryCache:
   self.cache: Dict[str, Dict[str, str]] = {}
   self.load()
 
- def load(self) -> None:
+ def load(self) -> Result[bool]:
   """
   Loads cache from disk.
   [C: src/tool_presets.py:ToolPresetManager._read_raw, src/workspace_manager.py:WorkspaceManager._load_file, tests/test_gui_phase3.py:test_create_track, tests/test_history_management.py:test_save_separation, tests/test_session_logging.py:test_open_session_creates_subdir_and_registry]
   """
-  if self.cache_file.exists():
+  if not self.cache_file.exists():
+   return Result(data=False)
   try:
    with open(self.cache_file, "r", encoding="utf-8") as f:
     self.cache = json.load(f)
-   except Exception:
+   return Result(data=True)
+  except (OSError, json.JSONDecodeError) as e:
    self.cache = {}
+   return Result(data=False, errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source="summary_cache.load", original=e)])
 
- def save(self) -> None:
+ def save(self) -> Result[bool]:
   """Saves cache to disk."""
   try:
    self.cache_file.parent.mkdir(parents=True, exist_ok=True)
    with open(self.cache_file, "w", encoding="utf-8") as f:
     json.dump(self.cache, f, indent=1)
-  except Exception:
+   return Result(data=True)
-   pass
+  except OSError as e:
+   return Result(data=False, errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source="summary_cache.save", original=e)])
 
  def get_summary(self, file_path: str, content_hash: str) -> Optional[str]:
   """
@@ -79,27 +85,29 @@ class SummaryCache:
    self.cache.pop(first_key)
   self.save()
 
- def clear(self) -> None:
+ def clear(self) -> Result[bool]:
   """
   Clears the cache both in-memory and on disk.
   [C: tests/conftest.py:reset_ai_client]
   """
   self.cache.clear()
-  if self.cache_file.exists():
+  if not self.cache_file.exists():
+   return Result(data=True)
   try:
    self.cache_file.unlink()
-   except Exception:
+   return Result(data=True)
-    pass
+  except OSError as e:
+   return Result(data=False, errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source="summary_cache.clear", original=e)])
 
- def get_stats(self) -> dict:
+ def get_stats(self) -> Result[dict]:
   """Returns dictionary of cache statistics."""
   size_bytes = 0
   if self.cache_file.exists():
    try:
     size_bytes = self.cache_file.stat().st_size
-   except Exception:
+   except OSError as e:
-    pass
+    return Result(data={"entries": len(self.cache), "size_bytes": 0}, errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=str(e), source="summary_cache.get_stats", original=e)])
-  return {
+  return Result(data={
    "entries": len(self.cache),
    "size_bytes": size_bytes
-  }
+  })