feat: backend native executor implement

internal/systemd/manager.go

@@ -0,0 +1,24 @@
+// Package systemd defines the exact systemd boundary used by native executors.
+package systemd
+
+import (
+	"context"
+	"errors"
+)
+
+var ErrUnitNotFound = errors.New("systemd unit not found")
+
+// Unit is the systemd state required for idempotent start and stop inspection.
+type Unit struct {
+	Name        string
+	LoadState   string
+	ActiveState string
+	SubState    string
+}
+
+// Manager performs direct systemd operations without invoking a shell.
+type Manager interface {
+	Inspect(context.Context, string) (Unit, error)
+	Start(context.Context, string) error
+	Stop(context.Context, string) error
+}