feat: share heaps and folders with other users, fix auth and vision pipeline

Sharing:
- New HeapShare and FolderShare models with read/write permissions
- Sharing API router (CRUD for heap and folder shares)
- Heap endpoints accept shared access (photo_ids, add/remove with write)
- Photo list drops user_id filter in shared context, adds owner_username
- Media serving (thumb/original/proxy) falls back to share check on 404
- ShareDialog component for managing shares from kebab menus
- HeapsPanel shows "Shared with me" section for shared heaps
- LeftSidebar shows "Shared with me" section for shared folders
- Owner badge on PhotoThumbnail for photos from other users

Auth:
- Access token default bumped to 1 year, refresh to 10 years
- Refresh token persisted in localStorage (survives page reload)
- Timer-based refresh replaced with 401 axios interceptor

Vision pipeline fixes:
- Bootstrap sets Redis ready key even on partial export failure
- Export functions run conditionally (only for actually missing models)
- _load_thumb handles multi-user path (/data/thumbs/{user_id}/{photo_id}/)
- can_access_photo_via_share uses single subquery instead of N+1 loop

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -9,6 +9,7 @@ from app.models.heaps import Heap, HeapPhoto
 from app.models.embeddings import Embedding
 from app.models.ocr_text import OCRText
 from app.models.face_embedding import FaceEmbedding
+from app.models.sharing import HeapShare, FolderShare
 
 __all__ = [
     'User',
@@ -22,4 +23,6 @@ __all__ = [
     'Embedding',
     'OCRText',
     'FaceEmbedding',
+    'HeapShare',
+    'FolderShare',
 ]