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/cli/set.go

@@ -0,0 +1,78 @@
+package cli
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+
+	"galahad2lcd/internal/config"
+	"galahad2lcd/internal/service"
+)
+
+func newSetCmd() *cobra.Command {
+	var (
+		configPath string
+		input      string
+		rotate     int
+		speed      float64
+		fps        float64
+		noRestart  bool
+	)
+
+	cmd := &cobra.Command{
+		Use:   "set",
+		Short: "Update display settings and restart the service",
+		Long: `Update the galahad2lcd configuration file and restart the systemd
+service. Provide at least one flag to change a setting. Writing the default
+configuration path requires root.`,
+		Args: cobra.NoArgs,
+		RunE: func(cmd *cobra.Command, _ []string) error {
+			if !cmd.Flags().Changed("input") &&
+				!cmd.Flags().Changed("rotate") &&
+				!cmd.Flags().Changed("speed") &&
+				!cmd.Flags().Changed("fps") {
+				return fmt.Errorf("nothing to set; provide at least one of --input, --rotate, --speed, --fps")
+			}
+
+			cfg, err := config.Load(configPath)
+			if err != nil {
+				return err
+			}
+			if err := applyOverrides(cmd, &cfg, input, rotate, speed, fps); err != nil {
+				return err
+			}
+			if err := cfg.Validate(); err != nil {
+				return fmt.Errorf("invalid configuration: %w", err)
+			}
+
+			if configPath == config.DefaultConfigPath && os.Geteuid() != 0 {
+				return fmt.Errorf("writing %s requires root (run with sudo)", configPath)
+			}
+			if err := cfg.Save(configPath); err != nil {
+				return err
+			}
+			fmt.Printf("configuration saved to %s\n", configPath)
+
+			if noRestart {
+				return nil
+			}
+
+			ctx, stop := newSignalContext()
+			defer stop()
+			if err := service.New(config.ServiceName).Restart(ctx); err != nil {
+				return err
+			}
+			fmt.Println("service restarted")
+			return nil
+		},
+	}
+
+	cmd.Flags().StringVar(&configPath, "config", config.DefaultConfigPath, "path to the configuration file")
+	cmd.Flags().StringVar(&input, "input", "", "path to the media file")
+	cmd.Flags().IntVar(&rotate, "rotate", 0, "rotation in degrees (0, 90, 180, 270)")
+	cmd.Flags().Float64Var(&speed, "speed", 0, "playback speed (>1 slower, <1 faster)")
+	cmd.Flags().Float64Var(&fps, "fps", 0, "output framerate (0 = auto)")
+	cmd.Flags().BoolVar(&noRestart, "no-restart", false, "do not restart the service after saving")
+	return cmd
+}