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/tasks/maintenance.py

@@ -1,4 +1,58 @@
-"""Maintenance-queue Celery tasks. Currently empty — the
-sync_character_fandoms task was removed on 2026-04-21 as part of the
-bare-name refactor (tag.fandom_id is now authoritative; no drift to sync).
+"""Maintenance-queue Celery tasks.
+
+Currently holds the blocklist cleanup task that retroactively removes
+blocklisted tag names from the library. The earlier sync_character_fandoms
+task was removed on 2026-04-21 as part of the bare-name refactor.
 """
+import logging
+
+from celery import shared_task
+from sqlalchemy import text
+
+from app import db
+from app.models import Tag
+
+log = logging.getLogger(__name__)
+
+
+@shared_task(
+    name='app.tasks.maintenance.sweep_blocklisted_tag_from_images',
+    soft_time_limit=60,
+    time_limit=120,
+)
+def sweep_blocklisted_tag_from_images(name: str) -> dict:
+    """Remove a blocklisted tag name from every image that has it attached,
+    then delete the Tag row itself.
+
+    Scope is limited to kind='user' tags — that's the kind WD14's general
+    category gets materialized as when accepted, which is the vast majority
+    of blocklist hits. Character / fandom / artist / series / post / archive
+    tags sharing the same name are left alone: those are deliberate, curated
+    entities, and removing them silently because of a blocklist text match
+    would be destructive.
+
+    Returns a summary dict so the Celery result is introspectable.
+    """
+    tag = Tag.query.filter_by(kind='user', name=name).first()
+    if tag is None:
+        log.info("sweep_blocklisted_tag_from_images: no kind='user' tag named %r; nothing to do", name)
+        return {'name': name, 'tag_found': False, 'image_tags_deleted': 0, 'tag_deleted': False}
+
+    result = db.session.execute(
+        text("DELETE FROM image_tags WHERE tag_id = :tid"),
+        {'tid': tag.id},
+    )
+    rowcount = result.rowcount or 0
+    db.session.delete(tag)
+    db.session.commit()
+
+    log.info(
+        "sweep_blocklisted_tag_from_images: removed %r (tag_id=%d) from %d images",
+        name, tag.id, rowcount,
+    )
+    return {
+        'name': name,
+        'tag_found': True,
+        'image_tags_deleted': rowcount,
+        'tag_deleted': True,
+    }