- Add pkce.ts with generatePKCE() using Web Crypto API
- Update anthropic.ts, google-gemini-cli.ts, google-antigravity.ts
- Replace Buffer.from() with atob() for base64 decoding
- Works in both Node.js 20+ and browsers
The OAuth modules still use Node.js http.createServer for callbacks,
so they only work in CLI environments, but they no longer crash on
import in browser bundles.
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