Live KC test WS, sync clock fix, device card perf, camera icons, tab indicator

Key Colors test:
- New WS endpoint for live KC target test streaming (replaces REST polling)
- Auto-connect on lightbox open, auto-disconnect on close
- Uses same FPS/preview_width as CSS source test (no separate controls)
- Removed FPS selector, start/stop toggle, and updateAutoRefreshButton

Device cards:
- Fix full re-render on every poll caused by relative "Last seen" time in HTML
- Last seen label now patched in-place via data attribute (like FPS metrics)
- Remove overlay visualization button from LED target cards

Sync clocks:
- Fix card not updating start/stop icon: invalidate cache before reload

Other:
- Tab indicator respects bg-anim toggle (hidden when dynamic background off)
- Camera backend icon grid uses SVG icons instead of emoji
- Frontend context rule: no emoji in IconSelect items

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

server/src/wled_controller/static/js/app.js

@@ -71,7 +71,7 @@ import {
     expandAllStreamSections, collapseAllStreamSections,
 } from './features/streams.js';
 import {
-    createKCTargetCard, testKCTarget, toggleKCTestAutoRefresh,
+    createKCTargetCard, testKCTarget,
     showKCEditor, closeKCEditorModal, forceCloseKCEditorModal, saveKCEditor,
     deleteKCTarget, disconnectAllKCWebSockets,
     updateKCBrightnessLabel, saveKCBrightness,
@@ -338,7 +338,6 @@ Object.assign(window, {
     // kc-targets
     createKCTargetCard,
     testKCTarget,
-    toggleKCTestAutoRefresh,
     showKCEditor,
     closeKCEditorModal,
     forceCloseKCEditorModal,