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

backend/app/api/ml_admin.py

@@ -9,12 +9,8 @@ ml_admin_bp = Blueprint("ml_admin", __name__, url_prefix="/api/ml")
 
 
 _EDITABLE = (
-    "suggestion_threshold_character",
-    "suggestion_threshold_general",
-    "tagger_store_floor",
     "video_frame_interval_seconds",
     "video_max_frames",
-    "video_min_tag_frames",
     "head_min_positives",
     "head_auto_apply_precision",
     "head_auto_apply_enabled",
@@ -37,13 +33,8 @@ async def get_settings():
         ).scalar_one()
     return jsonify(
         {
-            "suggestion_threshold_character": s.suggestion_threshold_character,
-            "suggestion_threshold_general": s.suggestion_threshold_general,
-            "tagger_store_floor": s.tagger_store_floor,
             "video_frame_interval_seconds": s.video_frame_interval_seconds,
             "video_max_frames": s.video_max_frames,
-            "video_min_tag_frames": s.video_min_tag_frames,
-            "tagger_model_version": s.tagger_model_version,
             "embedder_model_version": s.embedder_model_version,
             "head_min_positives": s.head_min_positives,
             "head_auto_apply_precision": s.head_auto_apply_precision,
@@ -88,31 +79,12 @@ async def patch_settings():
 
 
 def _validate(p: dict) -> str | None:
-    """Returns an error string if the proposed settings are invalid, else None.
-
-    Invariant (plan-task #764): the per-category suggestion thresholds can't
-    drop below tagger_store_floor — nothing below the floor is stored, so a
-    lower threshold would silently surface nothing in that gap. The UI clamps
-    the sliders to the floor; this is the server-side backstop.
-    """
-    floor = p["tagger_store_floor"]
-    if not (0.0 <= floor <= 1.0):
-        return "tagger_store_floor must be between 0 and 1"
-    for cat in ("character", "general"):
-        if p[f"suggestion_threshold_{cat}"] < floor:
-            return (
-                f"suggestion_threshold_{cat} cannot be below tagger_store_floor "
-                f"({floor}) — predictions below the floor are not stored"
-            )
-    # Video tagging (#747).
+    """Returns an error string if the proposed settings are invalid, else None."""
+    # Video embedding (#747).
     if p["video_frame_interval_seconds"] <= 0:
         return "video_frame_interval_seconds must be > 0"
     if p["video_max_frames"] < 1:
         return "video_max_frames must be >= 1"
-    if p["video_min_tag_frames"] < 1:
-        return "video_min_tag_frames must be >= 1"
-    if p["video_min_tag_frames"] > p["video_max_frames"]:
-        return "video_min_tag_frames cannot exceed video_max_frames"
     # Head training (#114).
     if int(p["head_min_positives"]) < 1:
         return "head_min_positives must be >= 1"