feat(dll): 自 go-hua 迁入 Windows 系统 API 封装

- 互斥体防多开/ShellExecute/窗口类名与标题查询/顶层窗口目录, 新增依赖 lxn/win
- 仅 Windows, 附测试、examples/dll 例程与包 README

dll/kernel32.go

@@ -0,0 +1,18 @@
+package dll
+
+import "syscall"
+
+// kernel32.dll 互斥体相关 API 函数指针
+var (
+	kernel32Dll      *syscall.DLL
+	procCreateMutexW *syscall.Proc
+	procOpenMutexW   *syscall.Proc
+	procReleaseMutex *syscall.Proc
+)
+
+func init() {
+	kernel32Dll = syscall.MustLoadDLL("kernel32.dll")
+	procCreateMutexW = kernel32Dll.MustFindProc("CreateMutexW")
+	procOpenMutexW = kernel32Dll.MustFindProc("OpenMutexW")
+	procReleaseMutex = kernel32Dll.MustFindProc("ReleaseMutex")
+}