Require Node 24 and npm 11

[hupponen]

npm versions resolve optional peer dependencies differently, which makes package-lock.json depend on the npm version that wrote it.

A concrete case: vite 8.2.2 has esbuild as an optional peer dependency. npm 11 leaves optional peers out of the lockfile, npm 10 installs them. A lockfile written by npm 11 therefore makes npm ci fail on npm 10 with Missing: esbuild@0.28.2 from lock file and 26 similar lines for its platform packages. Regenerating with npm 10 fixes that machine, but then the next npm install on npm 11 removes those 512 lines again, so the lockfile keeps flipping back and forth. This has happened before, see 86f04bb "Regenerate package-lock.json with npm 11.14.0".

The dev container and the production images use Node 24, which comes with npm 11, so declare that as the requirement instead of leaving it to whatever each developer happens to have installed.

Changes

• engines in package.json: node >= 24, npm >= 11
• .npmrc with engine-strict=true, because npm only warns by default and the resulting lockfile error is confusing to debug

Testing

• npm ci on Node 24.20.0 with npm 11.19.0: installs normally
• With engines.node temporarily set to >=99, npm ci fails as intended:

npm error code EBADENGINE
npm error notsup Required: {"node":">=99","npm":">=11"}
npm error notsup Actual:   {"node":"v24.20.0","npm":"11.19.0"}

• npm run build: production bundle builds

Anyone on an older Node now gets a clear error instead of a lockfile mismatch. Switching Node versions is easiest with nvm or asdf.