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/ipc/ipc.go

@@ -100,15 +100,26 @@ type Server struct {
 }
 
 // NewServer creates (but does not start) the IPC server. It removes
-// any stale socket file first.
+// any stale socket file first (unix only).
 func NewServer() (*Server, error) {
-	_ = os.Remove(paths.IPCSocketPath())
-	l, err := net.Listen("unix", paths.IPCSocketPath())
+	netType := paths.IPCNetwork()
+	addr := paths.IPCAddress()
+
+	// Clean up stale unix socket file (not needed for TCP).
+	if netType == "unix" {
+		_ = os.Remove(addr)
+	}
+
+	l, err := net.Listen(netType, addr)
 	if err != nil {
 		return nil, fmt.Errorf("listen ipc: %w", err)
 	}
-	// Mode 0660 so group members (admin) can connect.
-	_ = os.Chmod(paths.IPCSocketPath(), 0o660)
+
+	// Set socket permissions so group members can connect (unix only).
+	if netType == "unix" {
+		_ = os.Chmod(addr, 0o660)
+	}
+
 	return &Server{listener: l, clients: make(map[net.Conn]bool)}, nil
 }
 
@@ -178,7 +189,7 @@ type Client struct {
 
 // Dial connects to the daemon.
 func Dial() (*Client, error) {
-	conn, err := net.Dial("unix", paths.IPCSocketPath())
+	conn, err := net.Dial(paths.IPCNetwork(), paths.IPCAddress())
 	if err != nil {
 		return nil, fmt.Errorf("dial daemon: %w", err)
 	}