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/routers/photos.py

@@ -48,6 +48,7 @@ async def list_photos(
     color_label: Optional[str] = None,
     is_discarded: Optional[bool] = False,
     is_duplicate: Optional[bool] = None,
+    needs_review: Optional[bool] = None,
     has_date_warning: Optional[bool] = None,
     heap_id: Optional[str] = None,
     sort: str = "taken_at",
@@ -196,6 +197,8 @@ async def list_photos(
     # view shows everything regardless of duplicate status.
     if is_duplicate is not None:
         filters.append(Photo.is_duplicate == is_duplicate)
+    if needs_review is not None:
+        filters.append(Photo.needs_review == needs_review)
     if has_date_warning is not None:
         filters.append(Photo.has_date_warning == has_date_warning)