docs: state the supported Node.js versions and tested Nuxt releases

[sadjow]

The README now states which Node.js versions Nuxt UTM supports: the release lines the Node.js project still maintains, currently 22, 24, and 26. These are the versions the CI matrix already tests. Node.js 18 and 20 have reached end of life and are outside that set.

Support is documented, not enforced. The package still has no engines field. Yarn 1 fails an install when an engine range doesn't match, so a range would block apps on Nuxt releases that still accept Node.js 20, although no incompatibility is known. Nuxt and Nuxt Kit declare their own Node.js requirements, so any other version they accept stays installable but untested.

The same paragraph says which Nuxt releases CI tests: the latest Nuxt 3 and Nuxt 4 releases and Nuxt 5 nightly builds. Earlier minor releases are untested, but nothing blocks them. The module's compatibility.nuxt stays >=3.0.0 and the Nuxt Kit dependency stays ^3.17.2 || ^4.0.0. Nuxt disables a module whose compatibility range doesn't match the app, so narrowing either would switch capture off for existing apps with only a build warning.

The development section now refers to "each supported Node.js version" instead of repeating the list. When the CI matrix changes, only the Setup paragraph needs to change with it.

Release note: Node.js 22, 24, and 26 are supported, and CI tests the latest Nuxt 3 and 4 releases and Nuxt 5 nightly builds. Other versions are untested but not blocked at install time.

Validation: this changes only the README. prettier --check README.md passes. npm view nuxt-utm@0.4.0 engines returns nothing, so the published package doesn't restrict Node.js either, and @nuxt/kit@4 declares ^20.19.0 || >=22.12.0. The compatibility job's NUXT_VERSION values 3, 4, and npm:nuxt-nightly@5x resolve to Nuxt 3.21.11, 4.6.1, and a 5.0.0 nightly.