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/templates/settings.html

@@ -494,6 +494,24 @@
       </form>
     </section>
 
+    <section class="settings-section">
+      <h3>Apply auto-accepted predictions to all images</h3>
+      <p class="settings-hint">
+        Walks every image and applies general-category WD14 predictions
+        whose confidence is at or above the auto-accept threshold. Same
+        side-effects as opening each modal individually (creates the
+        kind='user' tag if needed, attaches it to the image, logs a
+        SuggestionFeedback rejection-protected record). Idempotent — safe
+        to re-run. Useful after a fresh ML backfill so high-confidence
+        tags land without needing to view each image. Skips images flagged
+        as integrity-corrupt.
+      </p>
+      <form action="{{ url_for('main.trigger_apply_auto_accept_predictions') }}" method="post"
+            onsubmit="return confirm('Apply every above-threshold general-category WD14 prediction to its image? This walks the entire library.');">
+        <button type="submit" class="btn secondary-btn">Apply auto-accepts library-wide</button>
+      </form>
+    </section>
+
     <section class="settings-section">
       <h3>Auto-accept threshold (general tags)</h3>
       <p class="settings-hint">