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/database.py

@@ -111,13 +111,7 @@ async def init_db():
     """Initialize database, create tables if they don't exist"""
     async with engine.begin() as conn:
         # Import all models to register them with Base
-        from app.models import User, Photo, Folder, SourceRoot, Tag, PhotoTag, Heap, HeapPhoto, Embedding
-
-        # Postgres: ensure pgvector is available before create_all touches
-        # any Vector columns (added in later PRs but the extension is cheap
-        # and idempotent to create now).
-        if _is_postgres:
-            await conn.execute(text("CREATE EXTENSION IF NOT EXISTS vector"))
+        from app.models import User, Photo, Folder, SourceRoot, Tag, PhotoTag, Heap, HeapPhoto  # noqa: F401
 
         # Create all tables. Note: create_all only creates *missing* tables —
         # it does NOT add new columns to existing tables when the model gains