feat: add displayName to package.json for proper UI display

Set displayName to 'Sealed Secrets' so the plugin settings list shows
the friendly name instead of the package name 'headlamp-sealed-secrets'.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

headlamp-sealed-secrets/package.json

@@ -1,5 +1,6 @@
 {
   "name": "headlamp-sealed-secrets",
+  "displayName": "Sealed Secrets",
   "version": "0.2.15",
   "description": "Headlamp plugin for Bitnami Sealed Secrets - manage encrypted Kubernetes secrets",
   "files": [