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/paths/paths_darwin.go

@@ -7,9 +7,11 @@ import (
 	"path/filepath"
 )
 
-// IPCSocketPath returns the path to the unix domain socket used for
-// GUI <-> daemon communication.
-func IPCSocketPath() string { return "/tmp/lmvpn.sock" }
+// IPCNetwork returns the transport network for GUI <-> daemon IPC.
+func IPCNetwork() string { return "unix" }
+
+// IPCAddress returns the listen/dial address for GUI <-> daemon IPC.
+func IPCAddress() string { return "/tmp/lmvpn.sock" }
 
 func init() {
 	home, _ := os.UserHomeDir()

internal/paths/paths_other.go

@@ -7,9 +7,11 @@ import (
 	"path/filepath"
 )
 
-// IPCSocketPath returns the path to the unix domain socket used for
-// GUI <-> daemon communication.
-func IPCSocketPath() string { return "/tmp/lmvpn.sock" }
+// IPCNetwork returns the transport network for GUI <-> daemon IPC.
+func IPCNetwork() string { return "unix" }
+
+// IPCAddress returns the listen/dial address for GUI <-> daemon IPC.
+func IPCAddress() string { return "/tmp/lmvpn.sock" }
 
 func init() {
 	home, _ := os.UserHomeDir()

internal/paths/paths_windows.go

@@ -7,12 +7,18 @@ import (
 	"path/filepath"
 )
 
-// IPCSocketPath returns the path to the unix domain socket used for
-// GUI <-> daemon communication. On Windows 10 1803+ AF_UNIX is
-// supported; the socket is placed in the user's temp directory.
-func IPCSocketPath() string {
-	return filepath.Join(os.TempDir(), "lmvpn.sock")
-}
+// IPCNetwork returns the transport network for GUI <-> daemon IPC.
+// Windows uses TCP because AF_UNIX sockets enforce mandatory
+// integrity-level checks: a socket created by the elevated daemon
+// (High Integrity) cannot be connected to by the non-elevated GUI
+// (Medium Integrity). TCP on 127.0.0.1 has no such restriction.
+func IPCNetwork() string { return "tcp" }
+
+// IPCAddress returns the listen/dial address for GUI <-> daemon IPC.
+// On Windows this is a TCP address on localhost.
+const ipcPort = "18923"
+
+func IPCAddress() string { return "127.0.0.1:" + ipcPort }
 
 func init() {
 	home, _ := os.UserHomeDir()