Add random streamer favorite requests

[Jamesllllllllll]

Summary

Add support for requesting a random song from the streamer's saved favorites pool across chat commands, the public web request surface, and the Twitch panel.

What Changed

• Added a shared favorite request mode alongside random and choice
• Treat !sr favorite and !sr favourite as random requests from the channel favorites pool
• Added minimal quick-request UI for random favorites on the web and Twitch panel
• Extended viewer and extension request validation to allow queryless favorite requests
• Added test coverage for request parsing, chat handling, viewer requests, and extension requests

How To Test

• In chat, request !sr favorite or !sr favourite and confirm it pulls from saved favorites
• In the web playlist page and Twitch panel, use the new favorite quick request option and confirm it adds a saved favorite without requiring artist input

Screenshots Or UI Notes

The web special-request control adds a single Favorite mode and disables the artist field while that mode is selected. The Twitch panel quick-request block adds one Random favorite row next to the existing random song and streamer choice actions.

Checklist

• I tested the change locally
• I updated docs or examples if needed
• I called out any follow-up work or known limitations

Follow-up: npm run lint still reports the repo's broader formatting baseline on many untouched files, but the changed files were formatted with the Biome wrapper and the repo's generated/typecheck/test pre-push checks passed.

[github-actions]

Preview deployment updated.

App: https://request-bot-pr-80.jameskeezer.workers.dev
Frontend worker: request-bot-pr-80
Backend worker: request-bot-backend-pr-80