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/css/modal.css

@@ -967,6 +967,31 @@
     background: var(--primary-color);
 }
 
+.lightbox-fps-select {
+    position: absolute;
+    top: 16px;
+    right: 116px;
+    background: rgba(0, 0, 0, 0.65);
+    color: #fff;
+    border: 1px solid rgba(255, 255, 255, 0.25);
+    border-radius: 6px;
+    padding: 4px 6px;
+    font-size: 0.8rem;
+    cursor: pointer;
+    z-index: 1;
+    appearance: none;
+    -webkit-appearance: none;
+    text-align: center;
+}
+
+.lightbox-fps-select:hover {
+    background: rgba(255, 255, 255, 0.15);
+}
+
+.lightbox-fps-select:focus {
+    outline: 1px solid var(--primary-color);
+}
+
 .lightbox-stats {
     position: absolute;
     bottom: 8px;