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/models/import_settings.py

@@ -116,6 +116,17 @@ class ImportSettings(Base):
         Float, nullable=False, default=0.9, server_default="0.9",
     )
 
+    # Title-based WIP auto-tagging (task #1458). When a freshly-imported post's
+    # TITLE explicitly declares work-in-progress ("WIP" / "work in progress"),
+    # the importer applies the `wip` system tag to its images — the artist's own
+    # label, used to keep unfinished pieces out of the Explore/gallery browse. ON
+    # by default (rule 26 — the feature works out of the box). Gates only the
+    # LIVE import hook; the existing catalogue is caught by the operator-triggered
+    # "Scan existing posts" backfill (which runs regardless of this flag).
+    wip_title_tagging_enabled: Mapped[bool] = mapped_column(
+        Boolean, nullable=False, default=True, server_default="true",
+    )
+
     @classmethod
     async def load(cls, session) -> ImportSettings:
         """The singleton settings row (id=1), via an async session."""