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/app.js

@@ -102,6 +102,7 @@ import {
 import {
     onDeviceTypeChanged, updateBaudFpsHint, onSerialPortFocus,
     showAddDevice, closeAddDeviceModal, scanForDevices, handleAddDevice,
+    cloneDevice,
 } from './features/device-discovery.js';
 import {
     loadTargetsTab, switchTargetSubTab,
@@ -123,6 +124,10 @@ import {
     mappedAddZone, mappedRemoveZone,
     onAudioVizChange,
     applyGradientPreset,
+    onGradientPresetChange,
+    promptAndSaveGradientPreset,
+    applyCustomGradientPreset,
+    deleteAndRefreshGradientPreset,
     cloneColorStrip,
     toggleCSSOverlay,
     previewCSSFromEditor,
@@ -130,6 +135,7 @@ import {
     onNotificationFilterModeChange,
     notificationAddAppColor, notificationRemoveAppColor,
     testNotification,
+    showNotificationHistory, closeNotificationHistory, refreshNotificationHistory,
     testColorStrip, testCSPT, closeTestCssSourceModal, applyCssTestSettings, fireCssTestNotification, fireCssTestNotificationLayer,
 } from './features/color-strips.js';
 
@@ -138,6 +144,7 @@ import {
     showAudioSourceModal, closeAudioSourceModal, saveAudioSource,
     editAudioSource, cloneAudioSource, deleteAudioSource,
     testAudioSource, closeTestAudioSourceModal,
+    refreshAudioDevices,
 } from './features/audio-sources.js';
 
 // Layer 5: value sources
@@ -177,6 +184,11 @@ import { openCommandPalette, closeCommandPalette, initCommandPalette } from './c
 import {
     openSettingsModal, closeSettingsModal, downloadBackup, handleRestoreFileSelected,
     saveAutoBackupSettings, restoreSavedBackup, downloadSavedBackup, deleteSavedBackup,
+    restartServer, saveMqttSettings,
+    loadApiKeysList,
+    downloadPartialExport, handlePartialImportFileSelected,
+    connectLogViewer, disconnectLogViewer, clearLogViewer, applyLogFilter,
+    loadLogLevel, setLogLevel,
 } from './features/settings.js';
 
 // ─── Register all HTML onclick / onchange / onfocus globals ───
@@ -240,6 +252,7 @@ Object.assign(window, {
     loadDevices,
     updateSettingsBaudFpsHint,
     copyWsUrl,
+    cloneDevice,
 
     // dashboard
     loadDashboard,
@@ -424,6 +437,10 @@ Object.assign(window, {
     mappedRemoveZone,
     onAudioVizChange,
     applyGradientPreset,
+    onGradientPresetChange,
+    promptAndSaveGradientPreset,
+    applyCustomGradientPreset,
+    deleteAndRefreshGradientPreset,
     cloneColorStrip,
     toggleCSSOverlay,
     previewCSSFromEditor,
@@ -431,6 +448,7 @@ Object.assign(window, {
     onNotificationFilterModeChange,
     notificationAddAppColor, notificationRemoveAppColor,
     testNotification,
+    showNotificationHistory, closeNotificationHistory, refreshNotificationHistory,
     testColorStrip, testCSPT, closeTestCssSourceModal, applyCssTestSettings, fireCssTestNotification, fireCssTestNotificationLayer,
 
     // audio sources
@@ -442,6 +460,7 @@ Object.assign(window, {
     deleteAudioSource,
     testAudioSource,
     closeTestAudioSourceModal,
+    refreshAudioDevices,
 
     // value sources
     showValueSourceModal,
@@ -504,7 +523,7 @@ Object.assign(window, {
     openCommandPalette,
     closeCommandPalette,
 
-    // settings (backup / restore / auto-backup)
+    // settings (backup / restore / auto-backup / MQTT / partial export-import / api keys / log level)
     openSettingsModal,
     closeSettingsModal,
     downloadBackup,
@@ -513,6 +532,17 @@ Object.assign(window, {
     restoreSavedBackup,
     downloadSavedBackup,
     deleteSavedBackup,
+    restartServer,
+    saveMqttSettings,
+    loadApiKeysList,
+    downloadPartialExport,
+    handlePartialImportFileSelected,
+    connectLogViewer,
+    disconnectLogViewer,
+    clearLogViewer,
+    applyLogFilter,
+    loadLogLevel,
+    setLogLevel,
 });
 
 // ─── Global keyboard shortcuts ───