Comprehensive WebUI review: 41 UX/feature/CSS improvements

Safety & Correctness:
- Add confirmation dialogs to Stop All, turnOffDevice
- i18n confirm dialog (title, yes, no buttons)
- Fix duplicate tutorial-overlay ID
- Define missing CSS variables (--radius, --text-primary, --hover-bg, --input-bg)
- Fix toast z-index conflict with confirm dialog (2500 → 3000)

UX Consistency:
- Add backdrop-close to test modals
- Add device clone feature (only entity without it)
- Add sync clocks to command palette
- Replace 20+ hardcoded accent colors with CSS vars/color-mix()
- Remove dead .badge duplicate from components.css
- Make calibration elements keyboard-accessible (div → button)
- Add aria-labels to color picker swatches
- Fix pattern canvas mobile horizontal scroll
- Fix graph editor mobile bottom clipping

Polish:
- Add empty-state messages to all CardSection instances
- Convert 21 px font-sizes to rem
- Add scroll-behavior: smooth with reduced-motion override
- Add @media print styles
- Add :focus-visible to 4 missing interactive elements
- Fix settings modal close label (Cancel → Close)
- Fix api-key submit button i18n

New Features:
- Command palette actions: start/stop targets, activate scenes, enable/disable
- Bulk start/stop API endpoints (POST /output-targets/bulk/start|stop)
- OS notification history viewer modal
- Scene "used by" automation reference count on cards
- Clock elapsed time display on Streams tab cards
- Device "last seen" relative timestamp on cards
- Audio device refresh button in edit modal
- Composite layer drag-to-reorder
- MQTT settings panel (broker config with JSON persistence)
- WebSocket log viewer with level filtering and ring buffer
- Runtime log-level adjustment (GET/PUT endpoints + settings UI)
- Animated value source waveform canvas preview
- Gradient custom preset save/delete (localStorage)
- API key read-only display in settings
- Backup metadata (file size, auto/manual badges)
- Server restart button with confirm + overlay
- Partial config export/import per entity type
- Progressive disclosure in target editor (Advanced section)

CSS Architecture:
- Define radius scale tokens (--radius-sm/md/lg/pill)
- Scope .cs-filter selectors to remove 7 !important overrides
- Consolidate duplicate toggle switch (filter-list → settings-toggle)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/wled_controller/templates/modals/calibration.html

@@ -81,16 +81,16 @@
                     </div>
 
                     <!-- Edge test toggle zones (outside container border, in tick area) -->
-                    <div class="edge-toggle toggle-top" onclick="toggleTestEdge('top')"></div>
-                    <div class="edge-toggle toggle-right" onclick="toggleTestEdge('right')"></div>
-                    <div class="edge-toggle toggle-bottom" onclick="toggleTestEdge('bottom')"></div>
-                    <div class="edge-toggle toggle-left" onclick="toggleTestEdge('left')"></div>
+                    <button type="button" class="edge-toggle toggle-top" onclick="toggleTestEdge('top')"></button>
+                    <button type="button" class="edge-toggle toggle-right" onclick="toggleTestEdge('right')"></button>
+                    <button type="button" class="edge-toggle toggle-bottom" onclick="toggleTestEdge('bottom')"></button>
+                    <button type="button" class="edge-toggle toggle-left" onclick="toggleTestEdge('left')"></button>
 
                     <!-- Corner start position buttons -->
-                    <div class="preview-corner corner-top-left" onclick="setStartPosition('top_left')">●</div>
-                    <div class="preview-corner corner-top-right" onclick="setStartPosition('top_right')">●</div>
-                    <div class="preview-corner corner-bottom-left" onclick="setStartPosition('bottom_left')">●</div>
-                    <div class="preview-corner corner-bottom-right" onclick="setStartPosition('bottom_right')">●</div>
+                    <button type="button" class="preview-corner corner-top-left" onclick="setStartPosition('top_left')">●</button>
+                    <button type="button" class="preview-corner corner-top-right" onclick="setStartPosition('top_right')">●</button>
+                    <button type="button" class="preview-corner corner-bottom-left" onclick="setStartPosition('bottom_left')">●</button>
+                    <button type="button" class="preview-corner corner-bottom-right" onclick="setStartPosition('bottom_right')">●</button>
 
                     <!-- Canvas overlay for ticks, arrows, start label -->
                     <canvas id="calibration-preview-canvas"></canvas>
@@ -141,7 +141,7 @@
             </div>
 
             <!-- Tutorial Overlay -->
-            <div id="tutorial-overlay" class="tutorial-overlay">
+            <div id="calibration-tutorial-overlay" class="tutorial-overlay">
                 <div class="tutorial-backdrop"></div>
                 <div class="tutorial-ring"></div>
                 <div class="tutorial-tooltip">