fix(build): fix tsdown external dependency regex on Windows (#626)

[shogun444]

What

Fixes #626.

The existing neverBundle regex (/^[^./]/) treats Windows drive-letter paths as external dependencies. During Windows builds this leaves local TypeScript imports unresolved in generated output, which later causes @openuidev/browser-bundle to fail with errors such as:

Could not resolve "./library.ts"
Could not resolve "./Renderer.tsx"

This change updates the regex so Windows absolute paths are handled correctly while preserving the existing behavior for package imports.

Changes

Updated the neverBundle configuration in the affected tsdown configs to avoid matching Windows absolute paths.

Test Plan

Tested on Windows 11.

pnpm install now completes successfully and @openuidev/browser-bundle builds without the unresolved import errors. I also verified that pnpm --filter @openuidev/docs dev starts successfully after the change.

[vishxrad]

LGTM.