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/locales/en.json

@@ -186,6 +186,10 @@
   "device.button.remove": "Remove",
   "device.button.webui": "Open Device Web UI",
   "device.button.power_off": "Turn Off",
+  "device.button.ping": "Ping Device",
+  "device.ping.online": "Online ({ms}ms)",
+  "device.ping.offline": "Device offline",
+  "device.ping.error": "Ping failed",
   "device.power.off_success": "Device turned off",
   "device.status.connected": "Connected",
   "device.status.disconnected": "Disconnected",