Add asset preprocessing filter and enhance asset data

Features:
- Filter unprocessed assets from events and get_assets service
  - Videos require completed transcoding (encodedVideoPath)
  - Photos require generated thumbnails (thumbhash)
- Add photo_url field for images (preview-sized thumbnail)
- Simplify asset attribute names (remove asset_ prefix)
- Prioritize user-added descriptions over EXIF descriptions

Documentation:
- Update README with new asset fields and preprocessing note
- Update services.yaml parameter descriptions

Version: 2.1.0

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

custom_components/immich_album_watcher/manifest.json

@@ -8,5 +8,5 @@
     "iot_class": "cloud_polling",
     "issue_tracker": "https://github.com/DolgolyovAlexei/haos-hacs-immich-album-watcher/issues",
     "requirements": [],
-    "version": "2.0.0"
+    "version": "2.1.0"
 }