feat: 支持 Windows x86_64 平台编译

- 新增 WinTun TUN 设备实现(tun_windows.go),无需安装驱动,
  wintun.dll 嵌入 exe 运行时自动释放
- 新增 Windows 路由管理(route_windows.go),使用 route/netsh 命令
- 新增 Windows 路径(paths_windows.go),使用 %APPDATA%/%LOCALAPPDATA%
- 拆分 daemon 启动逻辑:launch_unix.go(Setsid) / launch_windows.go
  (CREATE_NEW_PROCESS_GROUP),公共代码提取到 launch_common.go
- 拆分提权逻辑:elevation_darwin.go(osascript) / elevation_windows.go
  (ShellExecute UAC) / elevation_other.go(pkexec)
- IPCSocketPath 按平台分散,Windows 用 %TEMP%\lmvpn.sock
- daemon 二进制名用编译时常量(daemonBinaryName),按平台选定 .exe 后缀
- Makefile 新增 build-windows 目标
- 重新标记 !darwin 文件为 !darwin && !windows

internal/daemon/launch_common.go

@@ -0,0 +1,32 @@
+package daemon
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+// resolveDaemonBinary locates the lmvpnd binary relative to the
+// launcher's executable path. In a .app bundle, lmvpnd lives in the
+// same Contents/MacOS/ directory as lmvpn. In development, it lives
+// in the same build directory.
+func resolveDaemonBinary() (string, error) {
+	exe, err := os.Executable()
+	if err != nil {
+		return "", fmt.Errorf("resolve launcher executable: %w", err)
+	}
+
+	// Resolve any symlinks.
+	exe, err = filepath.EvalSymlinks(exe)
+	if err != nil {
+		return "", fmt.Errorf("resolve symlink: %w", err)
+	}
+
+	dir := filepath.Dir(exe)
+	candidate := filepath.Join(dir, daemonBinaryName)
+	if _, err := os.Stat(candidate); err == nil {
+		return candidate, nil
+	}
+
+	return "", fmt.Errorf("could not find %s near %s", daemonBinaryName, exe)
+}