Prepare 0.4.0 release

[Jamesllllllllll]

Summary

Prepare the 0.4.0 release workflow and documentation around the current app state.

What Changed

• audit and rewrite the active docs in present tense, and remove stale planning documents that have already been implemented
• bump the app version to 0.4.0 and move the shipped work into the 0.4.0 changelog entry
• add the deterministic ship workflow scripts, including check:ship and timestamped Twitch panel packaging
• add the request-bot-ship Codex skill and contributor guidance for commit messages and branch shipping
• tighten CI by adding i18n coverage checks and a standalone panel build

How To Test

1. Run npm run check:ship.
2. Run npm run build:extension:package.
3. Confirm the panel zip is written under output/twitch-extension/.
4. Review the updated docs and changelog for current-state wording.

Screenshots Or UI Notes

No end-user UI changes. This PR updates documentation, release metadata, repo scripts, and CI workflow coverage.

Checklist

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

[github-actions]

Preview deployment updated.

App: https://request-bot-pr-83.jameskeezer.workers.dev
Frontend worker: request-bot-pr-83
Backend worker: request-bot-backend-pr-83

[github-actions]

Preview deployment updated.

App: https://request-bot-pr-83.jameskeezer.workers.dev
Frontend worker: request-bot-pr-83
Backend worker: request-bot-backend-pr-83