feat(suggestions): auto-accept threshold + retroactive blocklist sweep

Two capabilities that work together to turn the suggestion system from
a 'review every noisy chip' UX into a 'curated tags only, configurable
auto-apply' UX for a solo-user library.

Auto-accept threshold
  Service (tag_suggestions.py):
    - New default auto_accept_general_threshold = 0.95 in _DEFAULTS
    - get_suggestions splits general-category hits at/above the threshold
      into a separate auto_accept_candidates list; the core 'character'/
      'copyright'/'general' keys stay the same shape for existing callers
    - get_bulk_suggestions ignores the new key (no side effects in bulk)
  Route (main.py GET /image/<id>/suggestions):
    - For each candidate: find-or-create Tag(kind='user', name=name), attach
      to image, log SuggestionFeedback(source='wd14'|etc, decision='accepted')
    - Response adds 'auto_accepted: [{id, name, display_name, kind,
      confidence, source}, ...]' so the modal can review + undo
  Config endpoints (main.py):
    GET  /api/suggestions/config/auto-accept-threshold
    POST /api/suggestions/config/auto-accept-threshold {threshold}
    Values > 1.0 effectively disable the feature
  UI (view-modal.js):
    - New renderAutoAccepted block at top of suggestions section with
      green-tinted chips carrying ✕ (undo for this image, logs rejection)
      and ⊘ (blocklist + remove from all images)
    - loadSuggestions refreshes the tag pill list when auto_accepted has
      items so the user sees them in the Tags section too
  Settings:
    - Maintenance tab gains a number input + save button backed by
      /api/suggestions/config/auto-accept-threshold

Retroactive blocklist sweep
  New Celery task app.tasks.maintenance.sweep_blocklisted_tag_from_images
  on the maintenance queue. Enqueued automatically when a name is added
  via POST /api/suggestions/blocklist or appears new in the bulk replace.
  Task body: finds kind='user' Tag matching the name, deletes its
  image_tags rows, deletes the Tag itself. Scope limited to kind='user'
  so deliberate character/fandom/artist tags sharing a blocklisted name
  aren't silently destroyed.

Verification (local dev):
  - Threshold GET/POST round-trip correct (default 0.95, persisted in
    tag_suggestion_config)
  - Image 633 at threshold=0.9: 4 general tags auto-applied, each with
    a SuggestionFeedback row, returned in auto_accepted
  - Blocklist add of 'sweeptestonly' with an attached test tag: Redis
    maintenance queue depth = 1, task body removes 1 image_tags row +
    the Tag row
  - get_bulk_suggestions still works (auto_accept_candidates key skipped)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/services/tag_suggestions.py

@@ -57,6 +57,10 @@ _DEFAULTS = {
     'threshold_meta':             0.5,
     'threshold_embedding':        0.85,
     'min_reference_images':       5.0,
+    # Above this confidence, general-category suggestions are auto-applied
+    # to the image by the route layer (see app.main.get_image_suggestions).
+    # Use 1.1 or greater to effectively disable. Default is conservative.
+    'auto_accept_general_threshold': 0.95,
     'wd14_model_version':         'wd-eva02-large-tagger-v3',
     'siglip_model_version':       'siglip-so400m-patch14-384',
 }
@@ -246,17 +250,34 @@ def get_suggestions(
     if existing_all is None:
         existing_all = _existing_tag_names()
 
+    # Separate out general-category suggestions above the auto-accept
+    # threshold. The route layer applies these to the image directly;
+    # we just identify them here so the service remains side-effect-free.
+    try:
+        auto_accept_threshold = float(cfg.get('auto_accept_general_threshold',
+                                              _DEFAULTS['auto_accept_general_threshold']))
+    except (TypeError, ValueError):
+        auto_accept_threshold = _DEFAULTS['auto_accept_general_threshold']
+    auto_accept_candidates: list[dict] = []
+
     grouped: dict[str, list[dict]] = {'character': [], 'copyright': [], 'general': []}
     for s in merged:
         if s['category'] not in grouped:
             continue  # meta / rating / artist / unknown are dropped
         s['exists_in_db'] = s['name'] in existing_all
+        if s['category'] == 'general' and s['confidence'] >= auto_accept_threshold:
+            auto_accept_candidates.append(s)
+            continue
         grouped[s['category']].append(s)
 
     for cat in grouped:
         grouped[cat].sort(key=lambda x: x['confidence'], reverse=True)
         grouped[cat] = grouped[cat][:top_k_per_category]
 
+    # Stash candidates in a way the shape documents but legacy callers can
+    # ignore. We keep the three core keys at the top level for backwards
+    # compat and add a 4th list.
+    grouped['auto_accept_candidates'] = auto_accept_candidates
     return grouped
 
 
@@ -308,6 +329,11 @@ def get_bulk_suggestions(
             existing_all=existing_all,
         )
         for category, items in grouped.items():
+            # `auto_accept_candidates` is returned by get_suggestions for the
+            # single-image route to apply; skip in bulk (bulk has no single
+            # image to attach to).
+            if category == 'auto_accept_candidates':
+                continue
             for item in items:
                 name = item['name']
                 stat = tag_stats.get(name)