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.go

@@ -0,0 +1,14 @@
+package platform
+
+import (
+	"context"
+	"os/signal"
+)
+
+// SignalContext returns a context canceled when an interactive termination
+// signal arrives: Ctrl+C on every OS, plus SIGTERM on Unix. It is the single
+// graceful-shutdown hook for the whole process.
+func SignalContext() (context.Context, context.CancelFunc) {
+	ctx, cancel := signal.NotifyContext(context.Background(), shutdownSignals()...)
+	return ctx, cancel
+}