`scriptShell` reached only `pnpm run` / `pnpm exec` (and `pnpm version`).
Every lifecycle script the install spawns passed `script_shell: None` and
so ran under the platform default, `sh` or `cmd`, however the workspace
had configured its shell. The TypeScript CLI threads `scriptShell` into
the same runs through `scriptsOpts`, so a workspace whose scripts assume
its configured shell worked there and not here.
Thread `config.script_shell` to the three contexts that spawn scripts
during an install: dependency build scripts, a project's own lifecycle
scripts, and `pnpm:devPreinstall`.
Deliberately unchanged, because the TypeScript CLI does not pass
`scriptShell` there either and matching it is the point:
- git-hosted dependency preparation (`install_package_by_snapshot`,
`patch`), whose counterpart `exec/prepare-package` builds its
`RunLifecycleHookOptions` without the field.
- `pack` and `publish` lifecycle scripts, likewise.
The tests spawn through a shell shim that records each script it is
handed, so a context that ignores the setting fails rather than silently
falling back to the default shell. Unix-only: the probe is a shell
script, and `select_shell` rejects `.cmd` / `.bat` shims on Windows.
