fix(init): use posix separators for the paths written into package.json

[KallinikosMil]

Summary

Running bob init on Windows writes backslashes into package.json:

{
  "main": "./lib\module\index.js",
  "types": "./lib\typescript\src\index.d.ts",
  "exports": {
    ".": {
      "types": "./lib\typescript\src\index.d.ts",
      "default": "./lib\module\index.js"
    }
  }
}

main, module, types and exports are module specifiers, not filesystem paths — they're always forward-slashed regardless of platform. main and types are lenient enough that some tooling still copes, but exports is matched as a literal string by Node's resolver, so a library initialised on Windows ships a manifest whose entry points don't resolve.

The values are built by interpolating path.join into a ./… template:

entries.module = `./${path.join(output, 'module', 'index.js')}`;

path.join is correct for touching the filesystem and wrong for producing a specifier. Since these are always relative and always forward-slashed, path.posix.join is the right join — five call sites, all feeding the same entries / types objects that main, module, types and exports are later derived from.

This is the same class of bug as callstack/react-native-paper#5054, where a platform-native path reached an import specifier.

Test plan

Windows 11, Node 22.23.2, yarn 4.11.0.

src/__tests__/init.test.ts already covers this — the committed snapshot encodes the correct forward-slash output, so on Windows it fails on main today:

Before

❯ src/__tests__/init.test.ts (1 test | 1 failed)
  × initializes the configuration

  - "main": "./lib/module/index.js",
  + "main": "./lib\module\index.js",

After — passes, without the snapshot being regenerated. The only file in the diff is init.ts; the snapshot is untouched, which is the point: the fix makes Windows produce exactly the output Linux and macOS already produce.

yarn lint and yarn typecheck are both clean, and the lefthook pre-commit (eslint + tsc) passed.

One thing that is not fixed here, and isn't yours

Two cases in typescript.test.ts still fail on my machine:

Error: EPERM: operation not permitted, symlink '…\bob-typescript-SA8Uzm' -> '…\consumer\node_modules\library'

That's a local privilege limitation, not a bug in this repo — Windows only allows fs.symlink with Developer Mode enabled or elevation, and I confirmed Developer Mode is off here (AllowDevelopmentWithoutDevLicense unset) and that a bare fs.symlinkSync fails the same way outside the repo entirely. I'm mentioning it only so the number of failing tests in the "before" output isn't confusing; I haven't touched those tests.

Worth noting the os matrices in build-local-libraries.yml and build-templates.yml are [ubuntu-latest, macos-latest], which is why this hasn't surfaced. Happy to add windows-latest in a separate PR if you'd like the coverage — I didn't want to spend your CI minutes without asking.