perf: reduce portable build size ~40MB — replace winsdk/wmi, migrate cv2 to Pillow

- Replace winsdk (~35MB) with winrt packages (~2.5MB) for OS notification
  listener. API is identical, 93% size reduction.
- Replace wmi (~3-5MB) with ctypes for monitor names (EnumDisplayDevicesW)
  and camera names (SetupAPI). Zero external dependency.
- Migrate cv2.resize/imencode/LUT to Pillow/numpy in 5 files (filters,
  preview helpers, kc_target_processor). OpenCV only needed for camera
  and video stream now.
- Fix DefWindowProcW ctypes overflow on 64-bit Python (pre-existing bug
  in platform_detector display power listener).
- Fix openLightbox import in streams-capture-templates.ts (was using
  broken window cast instead of direct import).
- Add mandatory data migration policy to CLAUDE.md after silent data
  loss incident from storage file rename without migration.

CLAUDE.md

@@ -48,6 +48,21 @@ Use `TODO.md` in the project root as the primary task tracker. **Do NOT use the
 
 **Use context7 MCP tools for library/framework documentation lookups** (FastAPI, OpenCV, Pydantic, yt-dlp, etc.) instead of relying on potentially outdated training data.
 
+## Data Migration Policy (CRITICAL)
+
+**NEVER rename a storage file path, store key, entity ID prefix, or JSON field name without writing a migration.** User data lives in JSON files under `data/`. If the code starts reading from a new filename while the old file still has user data, THAT DATA IS SILENTLY LOST.
+
+When renaming any storage-related identifier:
+1. **Add migration logic in `BaseJsonStore.__init__`** (or the specific store) that detects the old file/key and migrates data to the new name automatically on startup
+2. **Log a clear warning** when migration happens so the user knows
+3. **Keep the old file as a backup** after migration (rename to `.migrated` or similar)
+4. **Test the migration** with both old-format and new-format data files
+5. **Document the migration** in the commit message
+
+This applies to: file paths in `StorageConfig`, JSON root keys (e.g. `picture_targets` → `output_targets`), entity ID prefixes (e.g. `pt_` → `ot_`), and any field renames in dataclass models.
+
+**Incident context:** A past rename of `picture_targets.json` → `output_targets.json` was done without migration. The app created a new empty `output_targets.json` while the user's 7 targets sat unread in the old file. Data was silently lost.
+
 ## General Guidelines
 
 - Always test changes before marking as complete