Add VPS smoke test script

[Spbd1]

Motivation

• Provide a small, safe smoke test that can be run on a VPS to quickly verify the homepage, health endpoint, and optional token-protected admin API endpoints without exposing the admin token.

Description

• Add an executable Bash smoke test scripts/vps-smoke-test.sh (uses set -euo pipefail, default BASE_URL=http://127.0.0.1:3000, optional ADMIN_EXPORT_TOKEN) that checks GET / returns HTTP 200, GET /api/health returns HTTP 200 and JSON-like text, and (when ADMIN_EXPORT_TOKEN is set) GET /api/admin/diagnostics and GET /api/admin/stats return HTTP 200, printing clear PASS/FAIL lines and never printing the token; update docs/VPS_DEPLOYMENT.md with usage examples.

Testing

• Ran bash -n scripts/vps-smoke-test.sh and then the repository checks npm run typecheck, npm run lint, and npm run build, all of which completed successfully.

---

Codex Task