Use primary color for running node icons and fix add device modal dirty check

- Running graph nodes show entity icon in --primary-color instead of --text-muted
- Fix AddDeviceModal always showing dirty: serialize zones array with JSON.stringify
  for proper strict equality comparison (matching DeviceSettingsModal pattern)

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

server/src/wled_controller/static/js/features/device-discovery.js

@@ -28,7 +28,7 @@ class AddDeviceModal extends Modal {
             baudRate: document.getElementById('device-baud-rate').value,
             ledType: document.getElementById('device-led-type')?.value || 'rgb',
             sendLatency: document.getElementById('device-send-latency')?.value || '0',
-            zones: _getCheckedZones('device-zone-list'),
+            zones: JSON.stringify(_getCheckedZones('device-zone-list')),
             zoneMode: _getZoneMode(),
         };
     }