feat(photos): fix trash permanent delete and add empty trash

Permanently deleting a photo whose album was deleted failed because
authorization resolved through the album. Fall back to uploader
ownership when the photo is albumless. Add a bulk DELETE /trash that
removes every trashed photo the caller may delete (uncapped listing)
and returns the deleted count, with an «Очистить корзину» action on the
trash screen.

backend/internal/photos/store.go

@@ -341,6 +341,36 @@ func (s *Store) TrashCount(ctx context.Context, userID string) (int, error) {
 	return n, err
 }
 
+// ListTrashIdentities returns every trashed photo accessible to the user
+// (no display cap) so a bulk purge can authorize and remove each one.
+func (s *Store) ListTrashIdentities(ctx context.Context, userID string) ([]TrashIdentity, error) {
+	rows, err := s.pool.Query(ctx,
+		`SELECT p.id, COALESCE(p.album_id, ''), p.uploader_id
+		 FROM photos p
+		 LEFT JOIN albums a ON a.id = p.album_id
+		 WHERE p.deleted_at IS NOT NULL
+		   AND (
+		   	(a.id IS NOT NULL AND (a.owner_id = $1 OR EXISTS(
+		   		SELECT 1 FROM album_members m WHERE m.album_id = a.id AND m.user_id = $1)))
+		   	OR (p.album_id IS NULL AND p.uploader_id = $1)
+		   )
+		 ORDER BY p.deleted_at DESC`,
+		userID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []TrashIdentity{}
+	for rows.Next() {
+		var it TrashIdentity
+		if err := rows.Scan(&it.ID, &it.AlbumID, &it.UploaderID); err != nil {
+			return nil, err
+		}
+		out = append(out, it)
+	}
+	return out, rows.Err()
+}
+
 // RestoreToAlbum reassigns a soft-deleted photo to an album and clears the trash flag.
 func (s *Store) RestoreToAlbum(ctx context.Context, id, albumID string) error {
 	tag, err := s.pool.Exec(ctx,