All three schedulers now share a single persistent UniFi controller
connection instead of each creating a new login every 60-second cycle.
Reduces login attempts from 3/minute to 1 total, preventing fail2ban
lockouts on username/password auth controllers.

Session reconnects automatically on expiry (invalidated in error
handlers) and when config is saved via the web UI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>