`node:util.styleText` breaks browser compatibility

[yamcodes]

When importing arkenv in browser environments (Vite, Bun frontend), the library fails with a module externalization error:

Error: Module "node:util" has been externalized for browser compatibility. 
Cannot access "node:util.styleText" in client code.

Reproduction:

1. Import createEnv from arkenv in a Vite/Bun React component
2. Run the dev server
3. Error appears in browser console

Root Cause:

packages/arkenv/src/errors.ts imports styleText from node:util, which is Node-only.

Expected:

arkenv should work in both Node and browser environments without Node-specific dependencies.

Solution:

Replace node:util.styleText with a cross-platform alternative that works in browsers while maintaining zero dependencies.