Show both fps_current and fps_actual in WebUI charts and labels

- Charts: blue filled area for fps_actual (rolling avg), green line for
  fps_current (real-time sends/sec)
- Labels: fps_current/fps_target as primary, avg fps_actual as secondary
- Track fps_current in metrics history for dashboard chart preload
- Applied to both LED targets page and dashboard

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

server/src/wled_controller/core/processing/metrics_history.py

@@ -105,6 +105,7 @@ class MetricsHistory:
                 self._targets[target_id].append({
                     "t": now,
                     "fps": state.get("fps_actual"),
+                    "fps_current": state.get("fps_current"),
                     "fps_target": state.get("fps_target"),
                     "timing": state.get("timing_total_ms"),
                     "errors": state.get("errors_count", 0),