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/api/settings.py

@@ -49,6 +49,7 @@ _EDITABLE_FIELDS = (
     "translation_target_lang",
     "translation_min_confidence",
     "wip_title_tagging_enabled",
+    "wip_soft_title_tagging_enabled",
 )
 
 # Per-host external-download toggles — all plain booleans, validated uniformly.
@@ -91,6 +92,7 @@ async def get_import_settings():
         "translation_target_lang": row.translation_target_lang,
         "translation_min_confidence": row.translation_min_confidence,
         "wip_title_tagging_enabled": row.wip_title_tagging_enabled,
+        "wip_soft_title_tagging_enabled": row.wip_soft_title_tagging_enabled,
     })
 
 
@@ -179,6 +181,12 @@ async def update_import_settings():
         return jsonify(
             {"error": "wip_title_tagging_enabled must be a boolean"}
         ), 400
+    if "wip_soft_title_tagging_enabled" in body and not isinstance(
+        body["wip_soft_title_tagging_enabled"], bool
+    ):
+        return jsonify(
+            {"error": "wip_soft_title_tagging_enabled must be a boolean"}
+        ), 400
 
     async with get_session() as session:
         row = await ImportSettings.load(session)