Xlib's default protocol-error handler calls exit() on any async X error,
so a tray race (tray manager window dying between find and dock, XMoveWindow
on a popup the WM already destroyed) would take the whole UI process down.
Install process-global logging no-op handlers via XSetErrorHandler/
XSetIOErrorHandler after every XOpenDisplay. Since the handler slot is
process-global and GDK init can clobber it, additionally wrap the popup
code's raw Xlib calls on GDK's Display in gdk_x11_display_error_trap_push/
pop_ignored, which is independent of the global handler.
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.
