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

tests/test_wip_title.py

@@ -8,7 +8,7 @@ negative cases (substrings like ``swipe`` / ``wiped``) are the load-bearing ones
 """
 import pytest
 
-from backend.app.services.wip_title import matches_soft_wip_title, matches_wip_title
+from backend.app.services.wip_title import matches_wip_title
 
 
 @pytest.mark.parametrize("title", [
@@ -48,29 +48,3 @@ def test_matches_positive(title):
 ])
 def test_matches_negative(title):
     assert matches_wip_title(title) is False
-
-
-@pytest.mark.parametrize("title", [
-    "quick sketch",
-    "Nami sketch",
-    "morning doodle",
-    "some doodles",
-    "sketches from today",
-    "a little scribble",
-    "SKETCH",
-])
-def test_soft_matches_positive(title):
-    assert matches_soft_wip_title(title) is True
-
-
-@pytest.mark.parametrize("title", [
-    None,
-    "",
-    "sketchbook tour",              # 'sketch' inside sketchbook — must NOT match
-    "kadoodle mascot",              # 'doodle' mid-word
-    "the final piece",
-    "WIP",                          # a HARD cue is not a SOFT cue
-    "prescribed colours",           # 'scrib' inside prescribed — must NOT match
-])
-def test_soft_matches_negative(title):
-    assert matches_soft_wip_title(title) is False