feat: display platform agent status and version

prisma/schema.prisma

@@ -216,6 +216,9 @@ model ProvisionedDevice {
   kernel            String?
   distro            String?
   device            Json?
+  agentVersion      String?  @map("agent_version")
+  agentUpdatedAt    DateTime? @map("agent_updated_at") @db.Timestamptz(3)
+  agentLastSeenAt   DateTime? @map("agent_last_seen_at") @db.Timestamptz(3)
   installedAt       DateTime @default(now()) @map("installed_at") @db.Timestamptz(3)
   lastProvisionedAt DateTime @default(now()) @map("last_provisioned_at") @db.Timestamptz(3)
   createdAt         DateTime @default(now()) @map("created_at") @db.Timestamptz(3)
@@ -224,6 +227,7 @@ model ProvisionedDevice {
   @@unique([accountEmail, tailscaleHostname])
   @@index([accountEmail])
   @@index([tailscaleHostname])
+  @@index([agentLastSeenAt])
   @@map("provisioned_devices")
 }