feat(fc2b): importer enqueues tag_and_embed + ml-worker model self-heal

import_media_file now enqueues tag_and_embed alongside generate_thumbnail
after a successful import. scripts/download_models.py snapshots Camie +
SigLIP into /models, idempotent (skips when present). The ml-worker
entrypoint runs it before starting the Celery worker so a fresh /models
volume self-heals on first boot. Downloader tests are pure-logic (no
network in CI).

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

backend/app/tasks/import_file.py

@@ -95,11 +95,13 @@ def import_media_file(self, import_task_id: int) -> dict:
         session.add(task)
         session.commit()
 
-        # Enqueue the thumbnail task for newly imported images.
+        # Enqueue the thumbnail + ML tasks for newly imported images.
         if result.status == "imported" and result.image_id is not None:
+            from .ml import tag_and_embed
             from .thumbnail import generate_thumbnail
 
             generate_thumbnail.delay(result.image_id)
+            tag_and_embed.delay(result.image_id)
 
         # If this was the last task in the batch, mark the batch complete.
         remaining = session.execute(