Astro 6.x requires Node >=22.12.0. The previous Dockerfile used
node:20-alpine, which the Astro CLI rejected with:
Node.js v20.20.2 is not supported by Astro!
Please upgrade Node.js to a supported version: ">=22.12.0"
EasyPanel pulled the change, ran the build, and failed at
`RUN npm run build`. Bumping to node:22-alpine fixes it.
Also added two 'common failure' sections to docs/ci-setup.md
covering the nixpacks 'No start command' and Node version
mismatch errors we just hit.
21a538cbb8