`@Next/Codemod Upgrade` Writes Pnpm Overrides To Nested Workspace In Pnpm V11 Monorepos

The codemod writes pnpm v11 overrides relative to `cwd`, creating a new `pnpm-workspace.yaml` in the app folder. This marks the app as a separate workspace root, severing it from the monorepo siblings and breaking `pnpm install`.

1. Clone a pnpm v11 monorepo with an app depending on a workspace package via `workspace:*` and having `@types/react` / `@types/react-dom` installed. 2. Run `pnpm install` at root. 3. `cd` into the app directory. 4. Execute `pnpm dlx @next/codemod@canary upgrade latest` (or `pnpm exec next upgrade`). 5. Observe the created `apps/web/pnpm-workspace.yaml` and the install failure `ERR_PNPM_WORKSPACE_PKG_NOT_FOUND`.

This patch uses YAML parse/stringify, which may strip comments or custom formatting from an existing `pnpm-workspace.yaml`. Concurrent codemod runs could cause race conditions. If the root file contains complex YAML anchors or unknown keys, they might be lost. Rollback: back up the root `pnpm-workspace.yaml` before applying, and restore from version control if corruption occurs. Ensure the `yaml` package is available or replace with an already existing YAML parser.