refactor(ml): drop dead tagger/suggestion settings + columns (#1199)

Hygiene follow-up to the Camie retirement (#1189) — these were left inert to
bound that change; nothing reads them now. Migration 0068 drops:
- ml_settings: tagger_store_floor, tagger_model_version, suggestion_threshold_
  character/general (already dead pre-retirement — scoring uses per-head
  thresholds), video_min_tag_frames (only the deleted video-prediction
  aggregator used it).
- image_record: tagger_model_version (no writer), centroid_scores (dead JSON
  cache, no reader).

Also: ml_admin _EDITABLE/GET/_validate pruned (dropped the store-floor invariant
+ video_min_tag_frames check); MLThresholdSliders trimmed to a video-embedding
card (interval + max frames only); importer no longer resets the dropped cols;
download_models drops the Camie fetch; stale CASCADE comments in cleanup_service
no longer name the removed tables. Tests updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Ttrj5P7upUTueSfoJcxEqa

tests/test_migration_0003.py

@@ -20,12 +20,15 @@ def test_new_tables_registered():
 
 def test_image_record_columns_renamed():
     cols = {c.name for c in ImageRecord.__table__.columns}
-    # tagger_predictions (the renamed wd14_predictions) was later dropped in
-    # migration 0046 — predictions live in image_prediction now (#768).
-    assert "tagger_model_version" in cols
+    # Legacy tagger columns are all gone: tagger_predictions/wd14_* dropped in
+    # 0046, tagger_model_version + centroid_scores dropped in 0068 (#1199, Camie
+    # retirement). The SigLIP embedding columns are the live ML fields.
+    assert "siglip_embedding" in cols
+    assert "siglip_model_version" in cols
+    assert "tagger_model_version" not in cols
+    assert "centroid_scores" not in cols
     assert "tagger_predictions" not in cols
     assert "wd14_predictions" not in cols
-    assert "wd14_model_version" not in cols
 
 
 def test_tag_alias_composite_pk():