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/path.go

@@ -0,0 +1,32 @@
+package platform
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+// DefaultDataDir returns the OS-appropriate default data directory when the
+// user has not configured one. It never returns an empty path; on failure it
+// falls back to a relative "./data" directory.
+func DefaultDataDir() string {
+	home, err := os.UserHomeDir()
+	if err != nil {
+		return filepath.Join(".", "data")
+	}
+
+	switch runtime.GOOS {
+	case "windows":
+		if appdata := os.Getenv("APPDATA"); appdata != "" {
+			return filepath.Join(appdata, "Cyrene")
+		}
+		return filepath.Join(home, "AppData", "Roaming", "Cyrene")
+	case "darwin":
+		return filepath.Join(home, "Library", "Application Support", "Cyrene")
+	default:
+		if xdg := os.Getenv("XDG_DATA_HOME"); xdg != "" {
+			return filepath.Join(xdg, "cyrene")
+		}
+		return filepath.Join(home, ".local", "share", "cyrene")
+	}
+}