[client] Add Wails3 + React desktop UI scaffold

Stage 1 of the client/ui (Fyne) replacement. Adds a new client/ui-wails
module that runs on Linux/macOS/Windows from a single React + Vite +
Tailwind frontend driven by a thin gRPC services layer in Go.

- Single-module integration (no submodule): merge Wails3 into root go.mod
  with build tags !android !ios !freebsd !js so cross-compiles on those
  targets exclude the package automatically.
- Seven gRPC-bound services: Connection, Settings, Networks, Profiles,
  Debug, Update, Peers. Peers bridges Status polling and SubscribeEvents
  to the Wails event bus (netbird:status, netbird:event).
- Tray + window shell mirrors the Fyne menu 1:1 with hide-on-close,
  SIGUSR1 / Windows named-event for external "show window" triggers.
- React pages cover functional parity for Status, Settings (3 tabs),
  Networks (3 tabs), Profiles, Debug, Update, QuickActions, LoginUrl.
- SVG-sourced tray icons (12 source SVGs incl. macOS template variants)
  rasterized to PNG via task common:generate:tray:icons.
- Linux launcher sets WEBKIT_DISABLE_DMABUF_RENDERER=1 in the .desktop
  Exec= line and in task linux:run so the app renders correctly under
  RDP, VirtualBox, KVM, and bare WMs (Fluxbox/dwm) without DRM access.

client/ui-wails/frontend/src/components/Button.tsx

@@ -0,0 +1,42 @@
+import { ButtonHTMLAttributes, forwardRef } from "react";
+import { cn } from "../lib/cn";
+
+type Variant = "primary" | "secondary" | "ghost" | "danger";
+type Size = "sm" | "md";
+
+const variants: Record<Variant, string> = {
+  primary: "bg-netbird text-white hover:bg-netbird-500 disabled:bg-nb-gray-300",
+  secondary:
+    "bg-nb-gray-100 text-nb-gray-900 hover:bg-nb-gray-200 dark:bg-nb-gray-900 dark:text-nb-gray-50 dark:hover:bg-nb-gray-800",
+  ghost:
+    "bg-transparent text-nb-gray-700 hover:bg-nb-gray-100 dark:text-nb-gray-200 dark:hover:bg-nb-gray-900",
+  danger: "bg-red-600 text-white hover:bg-red-500",
+};
+
+const sizes: Record<Size, string> = {
+  sm: "h-7 px-2 text-xs",
+  md: "h-9 px-3 text-sm",
+};
+
+interface Props extends ButtonHTMLAttributes<HTMLButtonElement> {
+  variant?: Variant;
+  size?: Size;
+}
+
+export const Button = forwardRef<HTMLButtonElement, Props>(function Button(
+  { variant = "primary", size = "md", className, ...rest },
+  ref,
+) {
+  return (
+    <button
+      ref={ref}
+      className={cn(
+        "inline-flex items-center justify-center gap-2 rounded-md font-medium transition-colors disabled:cursor-not-allowed disabled:opacity-60",
+        variants[variant],
+        sizes[size],
+        className,
+      )}
+      {...rest}
+    />
+  );
+});