feat: add device connection status and owner username to device listings with handshake-based connectivity detection

Add connection_status and owner_username fields to Device model. Join users table in ListByUser and ListAll queries to populate owner_username from username column.

Parse latest_handshake_at from gateway runtime snapshots and aggregate across peers. Add isPeerConnected helper with 3-minute handshake timeout threshold. Set connection_status to "connected" or "disconnected" based on handsh

admin-web/src/api/client.ts

@@ -14,8 +14,10 @@ export type Device = {
   id: string;
   name: string;
   user_id?: string;
+  owner_username?: string;
   platform: string;
   status: string;
+  connection_status: string;
   assigned_ip?: string;
   rx_bytes: number;
   tx_bytes: number;

admin-web/src/features/devices/DevicesPage.tsx

@@ -7,6 +7,7 @@ import { Table } from "../../components/Table";
 const columns = [
   { key: "name", label: "Device" },
   { key: "owner", label: "Owner" },
+  { key: "connection", label: "Connection" },
   { key: "platform", label: "Platform" },
   { key: "ip", label: "VPN IP" },
   { key: "received", label: "Received" },
@@ -54,7 +55,8 @@ export function DevicesPage() {
   const rows = query.data?.map((device) => ({
     id: device.id,
     name: device.name,
-    owner: device.user_id ?? "assigned user",
+    owner: device.owner_username || device.user_id || "unassigned",
+    connection: device.connection_status === "connected" ? "Connected" : "Disconnected",
     platform: device.platform,
     ip: device.assigned_ip ?? "-",
     received: formatDataSize(device.rx_bytes ?? 0),