feat: Windows 安装器 + 修复 daemon 无法连接问题

- 新增 Inno Setup 安装器脚本 (installer/lmvpn.iss)，支持自定义安装路径、
  桌面快捷方式、安装前杀死旧进程，打包 wintun.dll
- Makefile 新增 installer-windows 目标，支持 ISCC 和 Wine 两种编译方式
- Windows IPC 从 AF_UNIX 改为 TCP (127.0.0.1:18923)，解决提权 daemon 与
  非提权 GUI 之间的完整性级别限制导致 daemon did not become reachable
- 修复 elevation_windows.go 中 ShellExecute 参数路径含空格时被截断的问题
  (C:\Program Files\LMVPN\lmvpnd.exe → 只取到 C:\Program)
- ensureDaemon 重试次数 40→60，添加连接失败日志便于诊断
- 新增 IPCNetwork()/IPCAddress() 跨平台函数，统一 IPC 传输层抽象

internal/daemon/daemon.go

@@ -60,8 +60,8 @@ func Run(userHome string, uid, gid int) error {
 	// Chown the IPC socket so the non-root GUI process can connect.
 	// This is the critical fix: without it, the socket is owned by
 	// root:wheel with mode 0660, and the user cannot dial it.
-	chownToUser(paths.IPCSocketPath(), uid, gid)
-	log.L().Info("daemon listening", "socket", paths.IPCSocketPath())
+	chownToUser(paths.IPCAddress(), uid, gid)
+	log.L().Info("daemon listening", "socket", paths.IPCAddress())
 
 	d := &daemon{server: server}