feat(maintenance): library-wide apply of auto-accept predictions

Adds a Celery task + Settings button that walks every image and applies
general-category WD14 predictions at or above the auto-accept threshold,
without needing the user to open each modal. Same side effects as the
modal's per-image auto-accept flow (creates kind='user' tag if needed,
attaches to image, writes SuggestionFeedback decision='accepted').

Lazy-imports app.services.tag_suggestions so the maintenance worker
doesn't pay its overhead unless this task fires. Amortizes _config()
and _existing_tag_names() across the loop. Commits per-batch (100
images) to keep transactions short and let later batches see freshly
created Tag rows.

Skips integrity-flagged images (get_suggestions already returns empty
for those). Idempotent — re-running just no-ops on already-applied
images via the existing 'tag not in img.tags' guard.

Trigger: Settings -> Maintenance -> "Apply auto-accepts library-wide"
(confirm-gated since it walks the entire library).

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

app/main.py

@@ -655,6 +655,16 @@ def trigger_sync_character_fandoms_to_images():
     return redirect(url_for('main.settings', tab='maintenance'))
 
 
+@main.post('/settings/maintenance/apply-auto-accept-predictions')
+def trigger_apply_auto_accept_predictions():
+    """Sweep every image, apply general WD14 predictions above the auto-accept
+    threshold without requiring the user to open each modal. One-shot —
+    intended to be run after a backfill drains."""
+    from app.tasks.maintenance import apply_auto_accept_predictions
+    apply_auto_accept_predictions.apply_async(queue='maintenance')
+    return redirect(url_for('main.settings', tab='maintenance'))
+
+
 @main.post('/settings/maintenance/verify-images')
 def trigger_verify_unverified_images():
     """Sweep ImageRecords and enqueue per-image structural verification.