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/locales/zh.json

@@ -80,6 +80,10 @@
   "templates.config.show": "显示配置",
   "templates.config.none": "无额外配置",
   "templates.config.default": "默认",
+  "templates.config.camera_backend.auto": "自动检测最佳后端",
+  "templates.config.camera_backend.dshow": "Windows DirectShow",
+  "templates.config.camera_backend.msmf": "Windows Media Foundation",
+  "templates.config.camera_backend.v4l2": "Linux Video4Linux2",
   "templates.created": "模板创建成功",
   "templates.updated": "模板更新成功",
   "templates.deleted": "模板删除成功",