[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/build/linux/desktop

@@ -0,0 +1,13 @@
+[Desktop Entry]
+Version=1.0
+Name=NetBird
+Comment=NetBird desktop client
+# The Exec line includes %u to pass the URL to the application
+Exec=/usr/local/bin/netbird-ui %u
+Terminal=false
+Type=Application
+Icon=netbird-ui
+Categories=Utility;
+StartupWMClass=netbird-ui
+
+