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/api/routes/picture_targets.py

@@ -33,7 +33,7 @@ from wled_controller.api.schemas.picture_targets import (
     TargetMetricsResponse,
     TargetProcessingState,
 )
-from wled_controller.config import config
+from wled_controller.config import get_config
 from wled_controller.core.capture_engines import EngineRegistry
 from wled_controller.core.filters import FilterRegistry, ImagePool
 from wled_controller.core.processor_manager import ProcessorManager, ProcessingSettings
@@ -763,8 +763,9 @@ async def target_colors_ws(
     """WebSocket for real-time key color updates. Auth via ?token=<api_key>."""
     # Authenticate
     authenticated = False
-    if token and config.auth.api_keys:
-        for _label, api_key in config.auth.api_keys.items():
+    cfg = get_config()
+    if token and cfg.auth.api_keys:
+        for _label, api_key in cfg.auth.api_keys.items():
             if secrets.compare_digest(token, api_key):
                 authenticated = True
                 break