[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/frontend/src/index.css

@@ -0,0 +1,17 @@
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+html,
+body,
+#root {
+  height: 100%;
+}
+
+body {
+  @apply bg-white text-nb-gray-900 antialiased;
+}
+
+.dark body {
+  @apply bg-nb-gray-950 text-nb-gray-50;
+}