The auto-update feature was driven by two narrow Wails events
(netbird:update:available and :progress) plus a SystemEvent-metadata
iteration on the React side. Both surfaces had to know the daemon
metadata schema (new_version_available, enforced, progress_window),
and the frontend had no pull endpoint to seed its state on mount.
Extract the state machine into a new client/ui/updater package, mirroring
how i18n and preferences are split between domain logic and a thin
services facade. The package owns the State type, the metadata-key
parsing, the mutex-guarded Holder, and the single netbird:update:state
event. services.Update keeps the daemon RPCs (Trigger, GetInstallerResult,
Quit) and gains GetState as a Wails pull endpoint.
Tray-side update behaviour moves out of tray.go into a dedicated
trayUpdater (tray_update.go): owns its menu item, OS notification,
click handler, and the /update window opener triggered by the
daemon's progress_window:show. tray.go drops three callbacks and four
fields, and reads hasUpdate through the updater.
Frontend ClientVersionContext now seeds from Update.GetState() and
subscribes to netbird:update:state; the status.events iteration and
metadata-key string literals are gone. UpdateAvailableBanner renders
only for the enforced && !installing branch and labels its action
"Install now"; UpdateVersionCard splits the install vs. download
branches by Enforced so the disabled flow routes to GitHub.
