feat: context menus, unified photo panel, tags, album trash and counters

- backend: deleting an album moves its photos to the trash without losing files (photos.album_id nullable, FK ON DELETE SET NULL, migration 000006; dropped S3 prefix delete); restore accepts an album target (album_required when the album is gone); user-scoped tags (000007) with GET /tags, POST/DELETE /photos/:id/tags, tags included in photo responses; GET /trash/count
- frontend: right-click context menus for photos (grid + viewer) and albums (rail + overview); single shared PhotoPanel reused in viewer and gallery selection (not a copy); viewer download/delete moved to the panel 'Действия'; transparent compact viewer top bar; trash entry as last rail item with per-album photo counts and trash count; album rename/delete dialogs
- openspec: sync lightroom-workspace-ui artifacts (specs photos/ui-workspace, design #24-30, tasks 9.17-9.24)

backend/migrations/000006_photo_album_nullable.down.sql

@@ -0,0 +1,5 @@
+ALTER TABLE photos DROP CONSTRAINT IF EXISTS photos_album_id_fkey;
+DELETE FROM photos WHERE album_id IS NULL;
+ALTER TABLE photos ALTER COLUMN album_id SET NOT NULL;
+ALTER TABLE photos ADD CONSTRAINT photos_album_id_fkey
+    FOREIGN KEY (album_id) REFERENCES albums(id) ON DELETE CASCADE;