Add Layouts module with Konva.js builder; smart offline polling; UI improvements

- Move board cards from dashboard to top of boards list page
- Fix Werkzeug duplicate polling (WERKZEUG_RUN_MAIN guard)
- Smart offline polling: fast loop for online boards, slow recheck for offline
- Add manual ping endpoint POST /api/boards/<id>/ping
- Add spin animation CSS for ping button

Layouts module (new):
- app/models/layout.py: Layout model (canvas_json, thumbnail_b64)
- app/routes/layouts.py: 5 routes (list, create, builder, save, delete)
- app/templates/layouts/: list and builder templates
- app/static/js/layout_builder.js: full Konva.js builder engine
- app/static/vendor/konva/: vendored Konva.js 9
- Structure mode: wall, room, door, window, fence, text shapes
- Devices mode: drag relay/input/Sonoff channels onto canvas
- Live view mode: click relays/Sonoff to toggle, socket.io state updates
- Device selection: click to select, remove individual device, Delete key
- Fix door/Arc size persistence across save/reload (outerRadius, scaleX/Y)
- Fix Sonoff devices missing from palette (add makeSonoffChip function)

app/templates/base.html

@@ -37,6 +37,12 @@
           <i class="bi bi-diagram-3 me-2"></i>Workflows
         </a>
       </li>
+      <li>
+        <a href="{{ url_for('layouts.list_layouts') }}"
+           class="nav-link text-white {% if 'layouts.' in request.endpoint %}active{% endif %}">
+          <i class="bi bi-map me-2"></i>Layouts
+        </a>
+      </li>
       {% if current_user.is_admin() %}
       <li>
         <a href="{{ url_for('admin.list_users') }}"