Add a dropdown on the admin dashboard to switch between update streams
(stable, rc, beta, alpha, development) matching the Joomla pattern.
Changes:
- Admin dashboard shows channel selector with descriptions
- POST handler validates and applies channel change in-memory
- Triggers immediate re-check against updates.xml after switch
- updates.xml has all 5 standard channels with descriptions
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Jonathan Miller
8509932b41