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/models/__init__.py

@@ -6,9 +6,6 @@ from app.models.photos import Photo
 from app.models.folders import Folder, SourceRoot
 from app.models.tags import Tag, PhotoTag
 from app.models.heaps import Heap, HeapPhoto
-from app.models.embeddings import Embedding
-from app.models.ocr_text import OCRText
-from app.models.face_embedding import FaceEmbedding
 from app.models.sharing import HeapShare, FolderShare
 
 __all__ = [
@@ -20,9 +17,6 @@ __all__ = [
     'PhotoTag',
     'Heap',
     'HeapPhoto',
-    'Embedding',
-    'OCRText',
-    'FaceEmbedding',
     'HeapShare',
     'FolderShare',
-]
+]