feat(deploy): add production runtime foundation

app/api/health/route.ts

@@ -0,0 +1,13 @@
+import { NextResponse } from "next/server";
+
+export async function GET() {
+  return NextResponse.json(
+    {
+      ok: true,
+      service: "plesk-agency-portal",
+      timestamp: new Date().toISOString(),
+      environment: process.env.NODE_ENV ?? "development",
+    },
+    { status: 200 },
+  );
+}