Tutorial: Deploy Directus to PandaStack (npm/Node + managed PostgreSQL)

## Summary

I'd like to contribute a new self-hosting tutorial — **Deploy Directus to PandaStack** — under `content/tutorials/6.self-hosting/`.

[PandaStack](https://pandastack.ai) is a Firecracker-microVM application platform with managed PostgreSQL. It deploys apps straight from a Git repository (install + start commands), so Directus runs as a plain **Node application** pointed at a managed Postgres — no Docker required.

## Why

The existing self-hosting tutorials in this folder (Railway, Render, AWS, Azure, GCP, DigitalOcean, Ubuntu) are all Docker/blueprint or raw-VM based. There isn't a pure **npm/Node PaaS** deploy guide yet. This tutorial fills that gap, and the flow is close in shape to the Railway and Render guides.

## What it covers

- Creating a managed PostgreSQL database
- A minimal repo: `package.json`, `pandastack.json`, `mise.toml`
- Environment variables (`DB_*` with `DB_SSL=true`, `KEY`, `SECRET`, `ADMIN_*`, `HOST`, `PORT`, `PUBLIC_URL`)
- Deploy and verify (admin login against the managed database)
- Optional: S3 storage for durable uploads, custom domain + TLS, importing an existing database

The whole flow was verified end to end on **Directus 12.2.0**, with admin login working against the managed PostgreSQL.

## Notes

Per `CONTRIBUTING.md` I'm opening this issue first for the core team's input — happy to adjust scope, tone, placement, or the example. One deploy detail worth surfacing: Directus's `isolated-vm` dependency relies on Node 22's prebuilt binary, so the tutorial pins Node 22 via `mise.toml`.

I've opened a PR with the tutorial and I'm glad to iterate on review.

The proposed tutorial belongs under content/tutorials/6.self-hosting/; review the existing Railway and Render guides first. Verify the documented Node 22, managed PostgreSQL, environment variables, deployment, and admin-login flow against Directus 12.2.0, and ensure the optional storage, domain/TLS, and database-import sections match the requested scope.

Written by the indexing model from the issue text.