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>

tests/test_download_models.py

@@ -0,0 +1,45 @@
+"""download_models tests. No network in CI; we test the 'already present →
+skip' short-circuit by faking the expected files, and that main() wires
+both ensure_* calls.
+"""
+
+from unittest.mock import patch
+
+from backend.app.scripts import download_models as dm
+
+
+def test_ensure_camie_skips_when_present(tmp_path, monkeypatch):
+    monkeypatch.setattr(dm, "MODEL_ROOT", tmp_path)
+    camie = tmp_path / "camie"
+    camie.mkdir(parents=True)
+    (camie / "model.onnx").write_bytes(b"x")
+    (camie / "selected_tags.csv").write_text("tag_id,name,category,count\n")
+    with patch.object(dm, "_snapshot") as snap:
+        dm.ensure_camie()
+        snap.assert_not_called()
+
+
+def test_ensure_camie_downloads_when_missing(tmp_path, monkeypatch):
+    monkeypatch.setattr(dm, "MODEL_ROOT", tmp_path)
+    with patch.object(dm, "_snapshot") as snap:
+        dm.ensure_camie()
+        snap.assert_called_once()
+
+
+def test_ensure_siglip_skips_when_present(tmp_path, monkeypatch):
+    monkeypatch.setattr(dm, "MODEL_ROOT", tmp_path)
+    sig = tmp_path / "siglip"
+    sig.mkdir(parents=True)
+    (sig / "config.json").write_text("{}")
+    (sig / "model.safetensors").write_bytes(b"x")
+    with patch.object(dm, "_snapshot") as snap:
+        dm.ensure_siglip()
+        snap.assert_not_called()
+
+
+def test_main_calls_both(monkeypatch):
+    calls = []
+    monkeypatch.setattr(dm, "ensure_camie", lambda: calls.append("camie"))
+    monkeypatch.setattr(dm, "ensure_siglip", lambda: calls.append("siglip"))
+    assert dm.main() == 0
+    assert calls == ["camie", "siglip"]