[client/ui] Replace fyne UI with Wails (rename ui-wails to ui)

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.

client/ui/xembed_host_other.go

@@ -0,0 +1,18 @@
+//go:build !linux || (linux && 386)
+
+package main
+
+import (
+	"errors"
+
+	"github.com/godbus/dbus/v5"
+)
+
+type xembedHost struct{}
+
+func newXembedHost(_ *dbus.Conn, _ string, _ dbus.ObjectPath) (*xembedHost, error) {
+	return nil, errors.New("XEmbed tray not supported on this platform")
+}
+
+func (h *xembedHost) run()  {}
+func (h *xembedHost) stop() {}