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/static/js/features/sync-clocks.js

@@ -190,6 +190,15 @@ export async function resetSyncClock(clockId) {
 
 // ── Card rendering ──
 
+function _formatElapsed(seconds) {
+    const s = Math.floor(seconds);
+    const h = Math.floor(s / 3600);
+    const m = Math.floor((s % 3600) / 60);
+    const sec = s % 60;
+    if (h > 0) return `${h}:${String(m).padStart(2, '0')}:${String(sec).padStart(2, '0')}`;
+    return `${m}:${String(sec).padStart(2, '0')}`;
+}
+
 export function createSyncClockCard(clock) {
     const statusIcon = clock.is_running ? ICON_START : ICON_PAUSE;
     const statusLabel = clock.is_running ? t('sync_clock.status.running') : t('sync_clock.status.paused');
@@ -197,6 +206,7 @@ export function createSyncClockCard(clock) {
         ? `pauseSyncClock('${clock.id}')`
         : `resumeSyncClock('${clock.id}')`;
     const toggleTitle = clock.is_running ? t('sync_clock.action.pause') : t('sync_clock.action.resume');
+    const elapsedLabel = clock.elapsed_time != null ? _formatElapsed(clock.elapsed_time) : null;
 
     return wrapCard({
         type: 'template-card',
@@ -211,6 +221,7 @@ export function createSyncClockCard(clock) {
             <div class="stream-card-props">
                 <span class="stream-card-prop">${statusIcon} ${statusLabel}</span>
                 <span class="stream-card-prop">${ICON_CLOCK} ${clock.speed}x</span>
+                ${elapsedLabel ? `<span class="stream-card-prop" title="${t('sync_clock.elapsed')}">⏱ ${elapsedLabel}</span>` : ''}
             </div>
             ${renderTagChips(clock.tags)}
             ${clock.description ? `<div class="template-config" style="opacity:0.7;">${escapeHtml(clock.description)}</div>` : ''}`,