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/internal/models/models.go

@@ -78,6 +78,7 @@ type Photo struct {
 	Longitude        *float64   `json:"longitude,omitempty"`
 	Caption          string         `json:"caption"`
 	EXIF             map[string]any `json:"exif,omitempty"`
+	Tags             []Tag          `json:"tags,omitempty"`
 	DeletedAt        *time.Time     `json:"deleted_at,omitempty"`
 	AlbumTitle       string         `json:"album_title,omitempty"`
 	CreatedAt        time.Time      `json:"created_at"`
@@ -91,6 +92,11 @@ type Photo struct {
 	DownloadURL      string     `json:"download_url,omitempty"`
 }
 
+type Tag struct {
+	ID   string `json:"id"`
+	Name string `json:"name"`
+}
+
 type Comment struct {
 	ID        string     `json:"id"`
 	PhotoID   string     `json:"photo_id"`