v2.2.1

v2.2.1: Polish release & Discord announcement upgrade

New:
- First-close tray education modal with 'Don't show again' preference
- Extension popup first-run guidance message
- Discord announcement system: auto changelog categorization,
  branded embed template, mention logic (patch/minor/major)
- RELEASE_AUTOMATION_REPORT.md & V2_2_1_POLISH_REPORT.md

Fixed:
- Window close-to-tray now shows educational dialog on first use
- Improved extension idle state messaging

Refactored:
- .github/workflows/discord-release.yml: full git history, Node.js
  changelog generation, structured embed payload