Integrated STS capability handling and connection lifecycle hooks (ignore CAP DEL, trigger upgrades, reschedule on disconnect, new server fields).
Initialized and cleaned up STS state during startup/shutdown to persist policies across sessions.
- Replaced the dark mode checkbox with an Auto/Dark/Light color mode selector and ensured palette edits use the resolved mode.
- Applied the resolved color mode consistently across palette saving and GTK styling in the user list and channel tree/theme application paths.