refactor: strip AI pipeline to binary photo/other classifier

Drops face recognition, OCR, object detection, and semantic embeddings.
The sole remaining vision task is a CLIP-based binary classifier
(photography vs other); photos in "other" get needs_review=true so
screenshots, documents, memes and scans can be triaged from a new
filter pill in the UI.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/schemas/photos.py

@@ -39,6 +39,7 @@ class PhotoResponse(PhotoBase):
     latitude: Optional[float] = None
     longitude: Optional[float] = None
     is_duplicate: bool = False
+    needs_review: bool = False
     has_date_warning: bool = False
     live_photo_video_id: Optional[str] = None
     owner_username: Optional[str] = None