When unlinking an Immich album, photos synced from that album are now
deleted. A new `album_link_id` FK column on `trip_photos` tracks the
source album link at sync time; `deleteAlbumLink` deletes matching
photos before removing the link. Individually-added photos are
unaffected. The client now refreshes the photo grid after unlinking.
Adds integration tests IMMICH-020 through IMMICH-024.
Closes#398