[Feature] Deletion Smart Sync From Native Photo App

I have searched the existing feature requests, both open and closed, to make sure this is not a duplicate request. • Yes The feature Problem Immich currently operates as a strict one-way backup tool (mobile to server). While this ensures server data is never accidentally deleted by local device changes, it creates a maintenance challenge over time: • Deleting photos in the native iOS/Android Photos app leaves them untouched on the server. • Over time, the server accumulates a large backlog of unwanted photos ("junk" or duplicates cleaned up on the phone). • Reviewing and sorting an entire server library manually on the web UI to find these items is cumbersome because there is no automated way to highlight what has already been discarded locally. Proposed Solution • Introduce an optional setting or workflow that leverages the existing mobile backup scan to flag assets that exist on the server but are no longer present on the mobile…