Root cause: instance_lite_restart was creating new thread without
re-setting g_event_handler, causing all chat events (CHANNEL_UPDATED,
CONNECT_RESULT, etc.) to be silently dropped after app restart.
Fixes:
- instance_lite_restart: save/restore g_event_handler across hard restart
- instance_thread restart loop: re-call chat_event_set_handler after uasync_create
- utun_bridge_restart: call instance_lite_set_event_handler before restart
- AppEventHandler SharedFlow replay: 1 → 16 to not lose early init events
- ViewModel: added diagnostic logging for channel/connect events
- Keep diagnostic logs in instance_lite (set_handler, chat_event_forward NULL check)
- instance_event_handler: removed static for cross-block forward declaration