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/scripts/__init__.py

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+"""Operational scripts run from the container entrypoint or CLI."""

backend/app/scripts/download_models.py

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+"""Self-heal model weights into /models. Idempotent — only missing files
+are fetched. Called by the ml-worker entrypoint before Celery starts.
+"""
+
+import os
+import sys
+from pathlib import Path
+
+MODEL_ROOT = Path(os.environ.get("ML_MODEL_DIR", "/models"))
+CAMIE_REPO = os.environ.get("CAMIE_HF_REPO", "Camais03/camie-tagger-v2")
+SIGLIP_REPO = os.environ.get(
+    "SIGLIP_HF_REPO", "google/siglip-so400m-patch14-384"
+)
+
+
+def _snapshot(repo_id: str, dest: Path, allow_patterns: list[str] | None) -> None:
+    from huggingface_hub import snapshot_download
+
+    dest.mkdir(parents=True, exist_ok=True)
+    snapshot_download(
+        repo_id=repo_id,
+        local_dir=str(dest),
+        allow_patterns=allow_patterns,
+    )
+
+
+def ensure_camie() -> None:
+    dest = MODEL_ROOT / "camie"
+    if (dest / "model.onnx").is_file() and (dest / "selected_tags.csv").is_file():
+        print(f"[download_models] Camie present at {dest}")
+        return
+    print(f"[download_models] Fetching {CAMIE_REPO} -> {dest}")
+    _snapshot(CAMIE_REPO, dest, ["model.onnx", "selected_tags.csv", "*.json"])
+
+
+def ensure_siglip() -> None:
+    dest = MODEL_ROOT / "siglip"
+    if (dest / "config.json").is_file() and any(dest.glob("*.safetensors")):
+        print(f"[download_models] SigLIP present at {dest}")
+        return
+    print(f"[download_models] Fetching {SIGLIP_REPO} -> {dest}")
+    _snapshot(SIGLIP_REPO, dest, None)
+
+
+def main() -> int:
+    ensure_camie()
+    ensure_siglip()
+    print("[download_models] Done.")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())