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/templates/settings.html

@@ -458,6 +458,23 @@
 
     </section>
 
+    <section class="settings-section">
+      <h3>Auto-accept threshold (general tags)</h3>
+      <p class="settings-hint">
+        When the modal loads suggestions for an image, any general-category
+        tag with confidence at or above this threshold is auto-applied and
+        shown in a reviewable "Auto-accepted" block at the top of the
+        suggestions section. Lower values accept more tags (riskier);
+        values above 1.0 effectively disable the feature. Default is 0.95.
+      </p>
+      <div class="mt-sm">
+        <input type="number" id="autoAcceptThresholdInput" class="settings-input"
+               min="0" max="1.1" step="0.01" style="width: 7rem;" />
+        <button type="button" id="autoAcceptThresholdSaveBtn" class="btn secondary-btn">Save threshold</button>
+        <span id="autoAcceptThresholdStatus" class="settings-hint" style="margin-left: 0.5rem;"></span>
+      </div>
+    </section>
+
     <section class="settings-section">
       <h3>Suggestion blocklist</h3>
       <p class="settings-hint">
@@ -465,8 +482,11 @@
         post-canonicalization WD14 output (e.g. <code>1girl</code>,
         <code>breasts</code>). Blocklisted names never appear in the
         modal's auto-suggestions — either WD14 or embedding-similarity
-        sourced. You can also add entries inline by clicking the ⊘ button
-        on any suggestion chip.
+        sourced. Adding a name also enqueues a cleanup task that removes
+        the tag from every image that has it attached (kind='user' only;
+        deliberate character / artist / fandom tags sharing the same name
+        are left alone). You can also add entries inline by clicking the
+        ⊘ button on any suggestion chip.
       </p>
       <textarea id="suggestionBlocklistArea" class="settings-textarea" rows="10"
                 placeholder="1girl&#10;2girls&#10;breasts&#10;nipples&#10;penis"></textarea>
@@ -521,6 +541,54 @@
   saveBtn.addEventListener('click', save);
   load();
 })();
+
+(function(){
+  const input   = document.getElementById('autoAcceptThresholdInput');
+  const saveBtn = document.getElementById('autoAcceptThresholdSaveBtn');
+  const status  = document.getElementById('autoAcceptThresholdStatus');
+  if (!input || !saveBtn) return;
+
+  async function load() {
+    try {
+      const r = await fetch('/api/suggestions/config/auto-accept-threshold');
+      const j = await r.json();
+      if (j.ok) input.value = String(j.threshold);
+    } catch { /* leave empty */ }
+  }
+
+  async function save() {
+    saveBtn.disabled = true;
+    status.textContent = 'Saving…';
+    const threshold = parseFloat(input.value);
+    if (isNaN(threshold) || threshold < 0) {
+      status.textContent = 'Enter a number >= 0 (use > 1 to disable).';
+      saveBtn.disabled = false;
+      return;
+    }
+    try {
+      const r = await fetch('/api/suggestions/config/auto-accept-threshold', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ threshold }),
+      });
+      const j = await r.json();
+      if (j.ok) {
+        status.textContent = `Saved (threshold = ${j.threshold}).`;
+        input.value = String(j.threshold);
+      } else {
+        status.textContent = 'Save failed: ' + (j.error || 'unknown');
+      }
+    } catch (e) {
+      status.textContent = 'Save failed: ' + e;
+    } finally {
+      saveBtn.disabled = false;
+      setTimeout(() => { status.textContent = ''; }, 4000);
+    }
+  }
+
+  saveBtn.addEventListener('click', save);
+  load();
+})();
 </script>
 {% endif %}