feat: NostrVPN mesh + VPN card UI + nvpn v0.3.7

- VPN card: relay URLs, device management, invite QR, add participant
- Backend: vpn.invite, vpn.add-participant, vpn.peer-config RPCs
- nvpn v0.3.7 system service (fixes event processing bug in v0.3.4)
- First-boot: auto-configure nvpn with node identity and endpoint
- Service: AF_NETLINK for WireGuard, NoNewPrivileges=no for sudo wg
- TASK-50: networking stack reliability from first install

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

neode-ui/src/api/rpc-client.ts

@@ -657,6 +657,11 @@ class RPCClient {
     bytes_out: number
     configured: boolean
     configured_provider: string
+    wg_ip?: string | null
+    node_npub?: string | null
+    relay_url?: string | null
+    relay_onion?: string | null
+    relay_direct?: string | null
   }> {
     return this.call({
       method: 'vpn.status',