feat(platform): 多平台检测/路径/信号/系统信息（含跨平台构建验证）

internal/platform/signal_windows.go

@@ -0,0 +1,11 @@
+//go:build windows
+
+package platform
+
+import "os"
+
+func shutdownSignals() []os.Signal {
+	// Windows has no SIGTERM equivalent; Ctrl+C (os.Interrupt) is the only
+	// portable interactive termination signal.
+	return []os.Signal{os.Interrupt}
+}