Windows target plans emit backslash paths in portable outputs

[ayskobtw-lil]

Running the target adapter test suite on Windows exposes several path normalization failures:

• tv-roku and web-static write manifest file lists with backslashes, e.g. assets\app.js, where the manifest contract expects portable / paths.
• pkg-jsr, plugin-vscode, and browser-safari convert POSIX-style project paths such as /repo/packages/my-lib into Windows root-relative paths such as \repo\packages\my-lib when constructing dry-run plans or mocked command cwd values.

This makes generated plans/manifests inconsistent across platforms and breaks the current tests on Windows.

I opened a fix in #443.