chore: retire the tag-eval harness — it proved the heads system, job done (operator-approved)

The head-vs-centroid eval (#1130) existed to prove the 'frozen embedding +
trained head' spine; the operator accepted the tagging system and dropped the
harness. Removed per rule 22: TagEvalCard + store, /api/tag_eval blueprint,
tag_eval_run ml task, recover-stalled-tag-eval-runs sweep + beat entry,
TagEvalRun model + table (migration 0073), and its tests.

The eval's data loaders + metric helpers were NOT eval-specific — the nightly
heads trainer runs on them — so they moved verbatim to
services/ml/training_data.py (heads.py import updated; behavior unchanged).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/api/__init__.py

@@ -38,7 +38,6 @@ def all_blueprints() -> list[Blueprint]:
     from .suggestions import suggestions_bp
     from .system_activity import system_activity_bp
     from .system_backup import system_backup_bp
-    from .tag_eval import tag_eval_bp
     from .tags import tags_bp
     from .thumbnails import thumbnails_bp
     return [
@@ -58,7 +57,6 @@ def all_blueprints() -> list[Blueprint]:
         import_admin_bp,
         suggestions_bp,
         aliases_bp,
-        tag_eval_bp,
         heads_bp,
         gpu_bp,
         ccip_bp,

backend/app/api/tag_eval.py

@@ -1,70 +0,0 @@
-"""Tag-eval API (#1130): trigger + revisit the head-vs-centroid eval.
-
-The run + full report live in the tag_eval_run row, so the admin card rehydrates
-from GET (history / detail) on mount — the report survives navigation rather than
-living in transient frontend state.
-"""
-
-from quart import Blueprint, jsonify, request
-from sqlalchemy import select
-
-from ..extensions import get_session
-from ..models import TagEvalRun
-from ..services.ml.tag_eval import EvalAlreadyRunning, start_tag_eval_run
-
-tag_eval_bp = Blueprint("tag_eval", __name__, url_prefix="/api/tag-eval")
-
-
-def _serialize(run: TagEvalRun, *, include_report: bool) -> dict:
-    out = {
-        "id": run.id,
-        "params": run.params,
-        "status": run.status,
-        "started_at": run.started_at.isoformat() if run.started_at else None,
-        "finished_at": run.finished_at.isoformat() if run.finished_at else None,
-        "error": run.error,
-    }
-    if include_report:
-        out["report"] = run.report
-    return out
-
-
-@tag_eval_bp.route("", methods=["POST"])
-async def create():
-    body = await request.get_json(silent=True) or {}
-    params = body.get("params") or body or {}
-    async with get_session() as session:
-        try:
-            run_id = await session.run_sync(
-                lambda s: start_tag_eval_run(s, params)
-            )
-        except EvalAlreadyRunning as running:
-            return jsonify({
-                "error": "eval_already_running",
-                "running_id": int(running.args[0]),
-            }), 409
-        await session.commit()
-    return jsonify({"run_id": run_id, "status": "running"}), 202
-
-
-@tag_eval_bp.route("", methods=["GET"])
-async def history():
-    try:
-        limit = min(int(request.args.get("limit", "20")), 100)
-    except ValueError:
-        return jsonify({"error": "invalid_limit"}), 400
-    async with get_session() as session:
-        rows = (await session.execute(
-            select(TagEvalRun).order_by(TagEvalRun.id.desc()).limit(limit)
-        )).scalars().all()
-        # List is light — no full report (the detail endpoint carries it).
-        return jsonify({"runs": [_serialize(r, include_report=False) for r in rows]})
-
-
-@tag_eval_bp.route("/<int:run_id>", methods=["GET"])
-async def detail(run_id: int):
-    async with get_session() as session:
-        run = await session.get(TagEvalRun, run_id)
-        if run is None:
-            return jsonify({"error": "not_found"}), 404
-        return jsonify(_serialize(run, include_report=True))