Port WLED optimizations to KC loop: fix FPS metrics, add keepalive and auto-refresh test

- Fix KC fps_actual to use frame-to-frame timestamps (was inflated by measuring before sleep)
- Add fps_potential, fps_current, frames_skipped, frames_keepalive metrics to KC loop
- Add keepalive broadcast for static frames so WS clients stay in sync
- Expose all KC metrics in get_kc_target_state() and update UI card to show 7 metrics
- Add auto-refresh play/pause button to KC test lightbox (polls every ~1s)
- Fix WebSocket color swatches computing hex from r,g,b when hex field is absent
- Fix WebSocket auth crash by using get_config() instead of module-level config variable
- Fix lightbox closing when clicking auto-refresh button (event bubbling)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/style.css

@@ -2440,6 +2440,33 @@ input:-webkit-autofill:focus {
     background: rgba(255, 255, 255, 0.3);
 }
 
+.lightbox-refresh-btn {
+    position: absolute;
+    top: 16px;
+    right: 64px;
+    background: rgba(255, 255, 255, 0.15);
+    border: none;
+    color: white;
+    font-size: 1.2rem;
+    width: 40px;
+    height: 40px;
+    border-radius: 50%;
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    transition: background 0.2s;
+    z-index: 1;
+}
+
+.lightbox-refresh-btn:hover {
+    background: rgba(255, 255, 255, 0.3);
+}
+
+.lightbox-refresh-btn.active {
+    background: var(--primary-color);
+}
+
 .lightbox-stats {
     position: absolute;
     bottom: 8px;