Major refactor: deduplicate routes, sync, JS, and fix bugs

- Extract 8 common route patterns into factory functions in routes/shared.py
  (favourite, upload, replace cover, save defaults, clone, save JSON,
  get missing, clear covers) — removes ~1,100 lines across 9 route files
- Extract generic _sync_category() in sync.py — 7 sync functions become
  one-liner wrappers, removing ~350 lines
- Extract shared detail page JS into static/js/detail-common.js — all 9
  detail templates now call initDetailPage() with minimal config
- Extract layout inline JS into static/js/layout-utils.js (~185 lines)
- Extract library toolbar JS into static/js/library-toolbar.js
- Fix finalize missing-image bug: raise RuntimeError instead of logging
  warning so job is marked failed
- Fix missing scheduler default in _default_checkpoint_data()
- Fix N+1 query in Character.get_available_outfits() with batch IN query
- Convert all print() to logger across services and routes
- Add missing tags display to styles, scenes, detailers, checkpoints detail
- Update delete buttons to use trash.png icon with solid red background
- Update CLAUDE.md to reflect new architecture

Net reduction: ~1,600 lines

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/gallery.html

@@ -332,10 +332,10 @@
            class="btn btn-sm btn-outline-light py-0 px-2"
            onclick="event.stopPropagation()">Generator</a>
         {% endif %}
-        <button class="btn btn-sm btn-outline-danger py-0 px-2"
+        <button class="btn btn-sm btn-danger py-0 px-2"
                 title="Delete"
                 onclick='event.stopPropagation(); openDeleteModal({{ img.path | tojson }}, {{ img.item_name | tojson }})'>
-          🗑
+          <img src="/static/icons/trash.png" alt="Delete" style="width:16px;height:16px;">
         </button>
       </div>
     </div>