Adds an end-to-end SSO session-extension feature: the management server
publishes per-peer session deadlines on every Login/Sync, a new
ExtendAuthSession RPC refreshes the deadline using a fresh JWT without
tearing down the tunnel, and the daemon tracks the deadline locally so
the UI can fire a T-10min warning toast with an interactive "Extend now"
action.
Removes the legacy fyne-based client/ui implementation and renames the
Wails replacement (client/ui-wails) to take its place at client/ui. Go
imports, frontend bindings, CI workflows, goreleaser configs and the
windows .syso icon path are updated to follow the rename.
Eduard Gert