Initial commit: Go driver for the Lian Li Galahad II LCD

Streams H.264 to the Galahad II LCD via USB (gousb) with:
- ffmpeg CLI transcoding (no fragile FFmpeg C-ABI bindings)
- pure-Go Annex-B access-unit splitting
- framerate pacing with graceful shutdown and USB reconnect
- TOML config, cobra CLI, structured slog logging, unit tests

internal/service/service.go

@@ -0,0 +1,34 @@
+// Package service manages the galahad2lcd systemd unit.
+package service
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+)
+
+// Service represents the installed systemd unit.
+type Service struct {
+	name string
+	// runCmd is the command constructor; overridable for tests.
+	runCmd func(ctx context.Context, name string, arg ...string) *exec.Cmd
+}
+
+// New returns a Service wrapper for the given unit name.
+func New(name string) *Service {
+	return &Service{name: name, runCmd: exec.CommandContext}
+}
+
+// Restart tells systemd to restart the service. It fails early when the
+// caller lacks privileges.
+func (s *Service) Restart(ctx context.Context) error {
+	cmd := s.runCmd(ctx, "systemctl", "restart", s.name)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		if len(out) > 0 {
+			return fmt.Errorf("systemctl restart %s: %w (%s)", s.name, err, string(out))
+		}
+		return fmt.Errorf("systemctl restart %s: %w", s.name, err)
+	}
+	return nil
+}