Add manual ping/health check button to device cards

Adds a refresh icon button on each device card that triggers an immediate
health check via POST /devices/{id}/ping, showing online status with
latency or offline result as a toast notification.

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

server/src/wled_controller/static/css/layout.css

@@ -147,6 +147,11 @@ h2 {
     to { transform: rotate(360deg); }
 }
 
+/* Device card ping button spinning animation */
+.card-ping-btn.spinning svg {
+    animation: conn-spin 0.8s linear infinite;
+}
+
 /* WLED device health indicator */
 .health-dot {
     display: inline-block;