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/static/css/cards.css

@@ -540,6 +540,15 @@ ul.section-tip li {
     font-size: 0.75rem;
 }
 
+.target-fps-avg {
+    display: block;
+    font-size: 0.65rem;
+    font-weight: 400;
+    opacity: 0.45;
+    line-height: 1.1;
+    color: #4CAF50;
+}
+
 /* Timing breakdown bar */
 .timing-breakdown {
     margin-top: 8px;

server/src/wled_controller/static/css/dashboard.css

@@ -171,6 +171,15 @@
     font-size: 0.75rem;
 }
 
+.dashboard-fps-avg {
+    display: block;
+    font-size: 0.6rem;
+    font-weight: 400;
+    opacity: 0.45;
+    line-height: 1.1;
+    color: #4CAF50;
+}
+
 .dashboard-target-actions {
     display: flex;
     align-items: center;