docs: Refresh AGENTS.md to reflect current deployment and workflow model

[Copilot]

The agent guidance file was outdated relative to recent repository changes. This updates AGENTS.md to match the current runtime, deployment, CI/CD, and command structure derived from recent commits.

• Runtime & deployment model

  • Replaced Vercel-era framing with the current Docker + Coolify model.
  • Documented Node 26/Yarn 4 runtime, multi-stage Docker build, and GHCR-based release flow.

• Architecture and API guidance

  • Added current operational details: Helmet + in-memory rate limiting, runtime Swagger generation, and test location.
  • Extended API overview with /_swagger-ui and versioned package request forms.

• Command and CI/CD alignment

  • Updated command list to current scripts (dist, start, start:prod, test, etc.).
  • Added concise CI/CD summary for lint/test/build, Docker linting, release publishing, and deploy trigger behavior.

## Runtime & Deployment
- **Runtime:** Node.js 26 + Yarn 4
- **Container:** Multi-stage Docker build (`Dockerfile`)
- **Distribution:** GitHub Container Registry image (no npm package release)
- **Deploy target:** Coolify (`lint_test_publish.yml` deploy job)