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/routers/admin.py

@@ -18,14 +18,6 @@ from app.models.user import User
 from app.models.photos import Photo
 from app.models.folders import SourceRoot
 from app.config import settings
-from app.services.feature_flags import (
-    ALL_FLAGS,
-    snapshot as flags_snapshot,
-    set_flag,
-    reset_flag,
-    is_enabled,
-    FLAG_VISION_ENABLED,
-)
 
 logger = logging.getLogger(__name__)
 
@@ -266,104 +258,3 @@ async def delete_user(
 
     logger.info(f"Admin '{admin.username}' deactivated user '{user.username}'")
     return {"status": "ok", "detail": f"User '{user.username}' deactivated"}
-
-
-# ---------------------------------------------------------------------------
-# AI / vision feature flags + manual triggers
-# ---------------------------------------------------------------------------
-
-class FeatureFlagUpdate(BaseModel):
-    """PATCH body for toggling a feature flag.
-
-    ``value`` sets an explicit override (true/false); omitting it clears
-    the override and reverts the flag to its YAML default.
-    """
-    value: Optional[bool] = None
-
-
-@router.get("/feature-flags")
-async def get_feature_flags(admin: User = Depends(require_admin)):
-    """Return every tunable feature flag with its current effective
-    value, YAML default, and whether an admin override is in effect."""
-    return {"flags": flags_snapshot()}
-
-
-@router.patch("/feature-flags/{flag_name}")
-async def update_feature_flag(
-    flag_name: str,
-    body: FeatureFlagUpdate,
-    admin: User = Depends(require_admin),
-):
-    """Set or clear an override for one flag. With ``value`` set, the
-    flag is pinned to that boolean; without it, the override is deleted
-    and the YAML default takes over again.
-
-    New value is observed by vision tasks on their next invocation —
-    there's no worker restart required.
-    """
-    if flag_name not in ALL_FLAGS:
-        raise HTTPException(status_code=404, detail=f"Unknown flag: {flag_name}")
-    try:
-        if body.value is None:
-            reset_flag(flag_name)
-            action = "cleared override"
-        else:
-            set_flag(flag_name, bool(body.value))
-            action = f"set to {body.value}"
-    except RuntimeError as e:
-        # Redis unreachable — surface as 503 so the UI doesn't think it
-        # succeeded silently.
-        raise HTTPException(status_code=503, detail=str(e))
-
-    logger.info(f"Admin '{admin.username}' {action} for flag '{flag_name}'")
-    return {"flags": flags_snapshot()}
-
-
-class BackfillVisionBody(BaseModel):
-    """POST body for triggering a classifier backfill. ``limit`` caps how
-    many photos are queued."""
-    limit: Optional[int] = None
-
-
-@router.post("/ai/backfill")
-async def trigger_ai_backfill(
-    body: BackfillVisionBody,
-    admin: User = Depends(require_admin),
-):
-    """Queue a classifier backfill pass."""
-    if not is_enabled(FLAG_VISION_ENABLED):
-        raise HTTPException(
-            status_code=400,
-            detail="Vision is currently disabled; enable it before running a backfill.",
-        )
-    if body.limit is not None and body.limit <= 0:
-        raise HTTPException(status_code=400, detail="limit must be positive")
-
-    from app.tasks.vision import backfill_vision
-
-    result = backfill_vision.apply_async(kwargs={'limit': body.limit})
-    logger.info(
-        f"Admin '{admin.username}' queued vision backfill "
-        f"(limit={body.limit}, celery_id={result.id})"
-    )
-    return {
-        "status": "queued",
-        "task_id": result.id,
-        "limit": body.limit,
-    }
-
-
-@router.post("/ai/rescan")
-async def trigger_full_rescan(admin: User = Depends(require_admin)):
-    """Dispatch the same scan_all_source_roots job the backend runs at
-    startup. Picks up any new files on disk and, through the
-    post-scan hook, queues a vision backfill for whatever still lacks
-    embeddings / OCR / etc.
-    """
-    from app.tasks.scan import scan_all_source_roots
-
-    result = scan_all_source_roots.apply_async()
-    logger.info(
-        f"Admin '{admin.username}' queued full rescan (celery_id={result.id})"
-    )
-    return {"status": "queued", "task_id": result.id}