Add Flip filter with bool option support and calibration UI polish

- New FlipFilter with horizontal/vertical bool options (np.fliplr/flipud)
- Add bool option type to filter system (base.py validate, app.js toggle UI)
- Rearrange calibration preview: direction toggle above LED count
- Normalize direction/offset control heights, brighten offset icon

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/locales/en.json

@@ -257,6 +257,7 @@
   "filters.downscaler": "Downscaler",
   "filters.pixelate": "Pixelate",
   "filters.auto_crop": "Auto Crop",
+  "filters.flip": "Flip",
   "postprocessing.description_label": "Description (optional):",
   "postprocessing.description_placeholder": "Describe this template...",
   "postprocessing.created": "Template created successfully",