Implement using PO token server to imrpove youtube downloads

[labithiotis]

Summary

• Add a Cloudflare Worker that provides YouTube Proof of Origin tokens at GET /token?videoId=....
• Cache tokens in Workers KV and use cold-start BotGuard tokens, with Browser Rendering as a fallback.
• Add CLI support for the token provider, including a persistent anonymous installation UUID, rate-limit handling, and --no-po-token.
• Pass returned PO token and visitor data into youtubei.js download sessions.
• Add Worker deployment workflow and document local Worker development.
• Add YouTube token smoke coverage plus CLI installation/network tests.
• Apply the repository formatting and cleanup changes included in this branch.

Validation

• bun lint
• bun typecheck
• bun test:unit
• Worker deployment dry run

Notes

• Worker access is abuse-controlled with anonymous installation and IP rate-limit identifiers; it is not authentication.
• The YouTube smoke test is manual because CI YouTube traffic can be blocked.