feat: retire the sketch/doodle WIP title tier, and the review strip asks "Is this a WIP?" (milestone 430)

The soft tier (#1474) tagged `wip` on any post titled sketch, doodle or
scribble: 6,096 of the library's 8,876 wip tags. Its conflict audit flagged
most of them, because finished art scores >= 0.5 on some content head,
which filled the Gallery strip with 2,086 cards. A "sketch" is usually
finished work, so the operator retired the tier. The artist's own
"WIP" / "work in progress" title rule and human wip tags stay.

- Removed: the soft matcher, source and prefilter; the importer and backfill
  soft branches; soft_wip_conflict_audit with its task and beat; the
  wip_soft_title_tagging_enabled setting, API field and toggle; and
  wip_title_soft from _AUTO_SOURCES.
- Migration 0112: a soft tag the operator confirmed, or kept from the strip,
  becomes `manual`. Every other soft tag is deleted, along with the open
  review cards whose tag is gone. The column is dropped.
- Review strip (#4424): each card asks "Is this a WIP?" (or banner, and so on),
  and the buttons read "Is a WIP" / "Is not a WIP". The content tag it also
  scored on is shown as the reason it was flagged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

backend/app/tasks/maintenance.py

@@ -1041,8 +1041,7 @@ def cleanup_old_download_events() -> int:
 
 def _backfill_wip_tier(session, tag_id, prefilter, matcher, source) -> int:
     """One keyset-paginated pass over posts whose title matches a WIP tier, applying
-    `tag_id` (stamped `source`) to their images. Shared by the hard + soft tiers
-    (#1458 / #1474). Coarse `prefilter` (ILIKE superset) narrows the scan; the precise
+    `tag_id` (stamped `source`) to their images (#1458). Coarse `prefilter` (ILIKE superset) narrows the scan; the precise
     `matcher` confirms. Idempotent-additive (ON CONFLICT DO NOTHING). Returns the row
     count newly applied."""
     from ..models import Post
@@ -1082,26 +1081,17 @@ def _backfill_wip_tier(session, tag_id, prefilter, matcher, source) -> int:
 )
 def backfill_wip_title_tags() -> int:
     """Scan EXISTING posts for WIP titles and apply the `wip` system tag to their
-    images — the operator-triggered back-catalogue catch-up (task #1458 hard tier +
-    #1474 soft tier). New imports are tagged live by the importer; this covers the
-    existing library.
-
-    HARD tier ("WIP"/"work in progress") always runs (the operator triggered the
-    scan); the SOFT tier (sketch/doodle, provisional source) runs only when
-    wip_soft_title_tagging_enabled, AFTER hard so a title matching both keeps the
-    trained hard tag (ON CONFLICT DO NOTHING). Keyset-paginated, restart-safe.
+    images — the operator-triggered back-catalogue catch-up (task #1458). New
+    imports are tagged live by the importer; this covers the existing library.
+    Keyset-paginated, restart-safe.
 
     Deliberately NOT scheduled as a beat: a periodic re-run would re-apply to matching
     posts and silently undo a manual WIP removal, so it stays an explicit operator
     action (Settings → "Scan existing posts for WIP titles"). Returns rows applied.
     """
-    from ..models import ImportSettings
     from ..services.wip_title import (
-        SOFT_WIP_TITLE_SQL_PREFILTER,
-        WIP_TITLE_SOFT_SOURCE,
         WIP_TITLE_SOURCE,
         WIP_TITLE_SQL_PREFILTER,
-        matches_soft_wip_title,
         matches_wip_title,
         resolve_wip_tag_id,
     )
@@ -1114,16 +1104,10 @@ def backfill_wip_title_tags() -> int:
                 "backfill_wip_title_tags: no `wip` system tag present; nothing to do"
             )
             return 0
-        settings = ImportSettings.load_sync(session)
         applied = _backfill_wip_tier(
             session, tag_id, WIP_TITLE_SQL_PREFILTER, matches_wip_title,
             WIP_TITLE_SOURCE,
         )
-        if settings.wip_soft_title_tagging_enabled:
-            applied += _backfill_wip_tier(
-                session, tag_id, SOFT_WIP_TITLE_SQL_PREFILTER, matches_soft_wip_title,
-                WIP_TITLE_SOFT_SOURCE,
-            )
     if applied:
         log.info("backfill_wip_title_tags: applied wip to %d image(s)", applied)
     return applied