#21864: chore: add .nvmrc file

Added a \.nvmrc\ file to precisely align the local developer environment with the \engines\ field specified in \package.json\. This helps contributors using \ vm\ to automatically switch to the correct Node.js environment by running \ vm use\. <!-- greptile_comment --> <h3>Greptile Summary</h3> Added `.nvmrc` file to help `nvm` users automatically switch to the correct Node.js version. However, the version specified (`22`) is less specific than the minimum requirement (`>=22.12.0` from `package.json` and enforced at `src/infra/runtime-guard.ts:12`), which could allow developers to use incompatible Node.js versions. <h3>Confidence Score: 3/5</h3> - This PR is safe to merge with minor risk - The change adds a useful `.nvmrc` file for developer convenience, but the version specified is too permissive and could lead to developers using incompatible Node.js versions that don't meet the minimum `22.12.0` requirement - `.nvmrc` should specify the full version `22.12.0` to match the minimum requirement _{Last reviewed commit: 3b45514} <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->