refactor(modules): improve exception handling and simplify service usage

Enhancements
- Replace bare `except:` with `except Exception:` in multiple modules- Cast step calculation to `int` for consistent type
- Simplify `get_battery_icon_file` to return a string directly
- Use `get_todo_service()` instead of module-level `todo_service` throughout todo widget
- Remove unused `"zen": "zen-browser"` mapping entry

Bug Fixes
- Prevent bare exception swallowing by catching `Exception` explicitly
- Ensure proper cleanup of timer IDs and other resources
- Delete unused modules/osdd components

New Features
- None

modules/notification/unified_cache.py

@@ -150,7 +150,7 @@ def verify_cache_persistence():
         for cache_file in cache_files[:2]:  # Test first 2 files
             try:
                 cache_path = os.path.join(UNIFIED_NOTIFICATION_CACHE_DIR, cache_file)
-                test_pixbuf = GdkPixbuf.Pixbuf.new_from_file(cache_path)
+                GdkPixbuf.Pixbuf.new_from_file(cache_path)
             except Exception as e:
                 logger.warning(f"Failed to load cached asset {cache_file}: {e}")
 
@@ -175,7 +175,7 @@ def get_fallback_icon(size=(48, 48)):
             return GdkPixbuf.Pixbuf.new(
                 GdkPixbuf.Colorspace.RGB, True, 8, size[0], size[1]
             )
-        except:
+        except Exception:
             return None