feat(wip): soft title tier — sketch/doodle vocab + ring-loud audit (#1474)

Extends WIP title-tagging to lower-precision cues (sketch/doodle/scribble) safely.

- wip_title.py: soft matcher (word-anchored; sketchbook/kadoodle don't trip it);
  WIP_TITLE_SOFT_SOURCE + soft SQL prefilter; apply_wip_image_tags takes a source arg.
- training_data._AUTO_SOURCES += 'wip_title_soft' → the soft tier is PROVISIONAL and
  never trains the wip head (a finished "sketch" can't pollute it). Only the hard
  tier (wip_title) + manual train.
- ImportSettings.wip_soft_title_tagging_enabled (OFF by default, opt-in). Migration 0087.
- importer: hard tier wins, soft is the fallback (source wip_title_soft).
- backfill: refactored into a shared _backfill_wip_tier; hard always, soft when enabled.
- heads.soft_wip_conflict_audit + daily beat: score soft-tagged images against content
  heads, flag ring-loud ones (PresentationReview mode=process) for the review strip —
  the operator's "measure if they got falsely tagged" safety.
- api settings toggle; ImportFiltersForm soft toggle.
- tests: soft matcher pos/neg; soft source not a training positive; audit flags
  ring-loud + spares quiet.

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

backend/app/tasks/ml.py

@@ -629,6 +629,24 @@ def scheduled_process_auto_apply() -> str:
     return f"applied={result['n_applied']} flagged={result['n_flagged']}"
 
 
+@celery.task(
+    name="backend.app.tasks.ml.scheduled_soft_wip_conflict_audit",
+    soft_time_limit=1800, time_limit=2100,
+)
+def scheduled_soft_wip_conflict_audit() -> str:
+    """Ring-loud audit over the SOFT WIP-title cohort (#1474) — flag sketch/doodle
+    auto-tags that ALSO look like real content for review. No-op when there are no
+    content heads; idempotent (already-flagged images skipped). Runs regardless of
+    the process-sweep toggle, since soft-title tags come from the importer, not that
+    sweep. Wall-clock bounded by the task time limits."""
+    from ..services.ml.heads import soft_wip_conflict_audit
+
+    SessionLocal = _sync_session_factory()
+    with SessionLocal() as session:
+        result = soft_wip_conflict_audit(session)
+    return f"scanned={result['n_scanned']} flagged={result['n_flagged']}"
+
+
 @celery.task(name="backend.app.tasks.ml.prune_presentation_reviews")
 def prune_presentation_reviews() -> str:
     """Retention (rule 89): drop RESOLVED presentation-review flags older than 30