feat(tagging): title-based WIP auto-tagging (#1458)

Auto-apply the `wip` system tag to posts whose TITLE explicitly declares
work-in-progress ("WIP" / "work in progress") — a deterministic, high-precision
complement to the image-based ML `wip` head. WIP images are excluded from the
Explore/gallery browse, so honouring the artist's own label keeps unfinished
pieces out of the main browse.

- services/wip_title.py: precision-first token-anchored matcher (swipe/wiped
  never trip it) + sync apply helpers (source='wip_title', ON CONFLICT DO
  NOTHING, chunked under the psycopg param ceiling).
- importer: live hook on FRESH import only (never on deep-scan/supersede), so a
  manually-removed WIP tag is never re-applied by a routine re-scan.
- maintenance.backfill_wip_title_tags: operator-triggered back-catalogue sweep
  (coarse SQL prefilter + regex confirm, keyset-paginated). Deliberately NOT a
  beat — a periodic re-run would silently undo manual removals.
- ImportSettings.wip_title_tagging_enabled (default ON, migration 0085) gating
  the live hook; GET/PATCH + POST /settings/wip-title/scan.
- Settings UI: toggle + "Scan existing posts" button.
- Tests: pure matcher unit tests + integration (apply idempotency, backfill
  precision).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/app/api/settings.py

@@ -48,6 +48,7 @@ _EDITABLE_FIELDS = (
     "interpreter_base_url",
     "translation_target_lang",
     "translation_min_confidence",
+    "wip_title_tagging_enabled",
 )
 
 # Per-host external-download toggles — all plain booleans, validated uniformly.
@@ -89,6 +90,7 @@ async def get_import_settings():
         "interpreter_base_url": row.interpreter_base_url,
         "translation_target_lang": row.translation_target_lang,
         "translation_min_confidence": row.translation_min_confidence,
+        "wip_title_tagging_enabled": row.wip_title_tagging_enabled,
     })
 
 
@@ -171,6 +173,12 @@ async def update_import_settings():
             return jsonify(
                 {"error": "series_suggest_threshold must be a number in [0, 1]"}
             ), 400
+    if "wip_title_tagging_enabled" in body and not isinstance(
+        body["wip_title_tagging_enabled"], bool
+    ):
+        return jsonify(
+            {"error": "wip_title_tagging_enabled must be a boolean"}
+        ), 400
 
     async with get_session() as session:
         row = await ImportSettings.load(session)
@@ -182,6 +190,18 @@ async def update_import_settings():
     return await get_import_settings()
 
 
+@settings_bp.route("/settings/wip-title/scan", methods=["POST"])
+async def wip_title_scan():
+    """Enqueue the back-catalogue WIP-title scan (task #1458 Settings button):
+    apply the `wip` system tag to EXISTING posts whose title declares
+    work-in-progress. New imports are tagged live by the importer; this catches
+    the existing library. Returns the Celery task id (202)."""
+    from ..tasks.maintenance import backfill_wip_title_tags
+
+    r = backfill_wip_title_tags.delay()
+    return jsonify({"celery_task_id": r.id}), 202
+
+
 @settings_bp.route("/system/stats", methods=["GET"])
 async def system_stats():
     async with get_session() as session: