refactor: drop AI/vision pipeline + plain Postgres + full-refresh script

Removes the OpenCLIP-on-ONNX classifier and everything that fed or
consumed it:
  - backend: app/services/vision/, app/tasks/vision.py,
    app/services/feature_flags.py, app/routers/features.py — all
    deleted; admin AI/feature-flag endpoints and the worker-vision
    bootstrap call gone. Photo.needs_review and its index dropped.
  - frontend: AI Settings tab, useFeaturesQuery hook, FeatureFlag
    types, "Needs Review" sidebar entry + filter, needs_review filter
    URL param all gone.
  - infra: worker-vision compose service + models_data volume deleted;
    worker-light command no longer runs bootstrap_models; the db
    image switches from pgvector/pgvector:pg16 to postgres:16; backend
    Dockerfile drops the dedicated torch RUN layer; requirements.txt
    drops torch/torchvision/open-clip-torch/onnxruntime.

Alembic 0019_drop_ai_remnants:
  - drops photos.needs_review + ix_photos_needs_review
  - DROP EXTENSION IF EXISTS vector (must run before the image swap;
    the new postgres:16 doesn't ship pgvector)

New scripts/full_refresh.py: one-shot DB ↔ filesystem reconciliation.
Runs cleanup_data_integrity, scans every active SourceRoot inline
(no celery dependency so the worker can be stopped), hard-prunes
photo + folder rows for files that are gone, removes orphan
/data/thumbs/{user}/{photo}/ directories. New helper
prune_orphan_thumbnails in cleanup.py.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/services/cleanup.py

@@ -299,6 +299,65 @@ async def prune_missing_photos(dry_run: bool = True) -> dict:
             raise
 
 
+async def prune_orphan_thumbnails(
+    thumbs_root: str = "/data/thumbs",
+    dry_run: bool = True,
+) -> dict:
+    """Remove `/data/thumbs/{user_id}/{photo_id}/` directories whose
+    photo_id no longer exists in the photos table.
+
+    Layout was per-Phase-4 set up by app.tasks.thumbs and is keyed by
+    `{user_id}/{photo_id}/`. The thumbs worker never deletes its own
+    output on photo removal, so over the lifetime of a library these
+    directories accumulate.
+
+    Set dry_run=False to actually `rm -rf` each matched directory.
+    Returns counts of matched / removed dirs and any per-dir errors.
+    """
+    import shutil
+
+    if not os.path.isdir(thumbs_root):
+        return {
+            "would_remove": 0,
+            "removed": 0,
+            "skipped_no_root": True,
+            "dry_run": dry_run,
+        }
+
+    async with AsyncSessionLocal() as session:
+        live_ids = {
+            row[0]
+            for row in (await session.execute(select(Photo.id))).all()
+        }
+
+    matched: list[str] = []
+    errors: list[str] = []
+    for user_dir in os.listdir(thumbs_root):
+        user_path = os.path.join(thumbs_root, user_dir)
+        if not os.path.isdir(user_path):
+            continue
+        for photo_dir in os.listdir(user_path):
+            if photo_dir in live_ids:
+                continue
+            matched.append(os.path.join(user_path, photo_dir))
+
+    removed = 0
+    if not dry_run:
+        for path in matched:
+            try:
+                shutil.rmtree(path)
+                removed += 1
+            except OSError as e:
+                errors.append(f"{path}: {e}")
+
+    key = "would_remove" if dry_run else "removed"
+    return {
+        key: len(matched) if dry_run else removed,
+        "errors": errors,
+        "dry_run": dry_run,
+    }
+
+
 async def discard_missing_photos() -> dict:
     """Soft variant of prune_missing_photos for the periodic beat
     catch-up. Walks every active source root that is currently