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/flags.go

@@ -0,0 +1,48 @@
+package cli
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/spf13/cobra"
+
+	"galahad2lcd/internal/config"
+)
+
+// applyOverrides merges explicitly provided flags into cfg. Zero-valued
+// flags are ignored unless the user actually changed them.
+func applyOverrides(cmd *cobra.Command, cfg *config.Config, input string, rotate int, speed, fps float64) error {
+	if cmd.Flags().Changed("input") {
+		abs, err := resolveInput(input)
+		if err != nil {
+			return err
+		}
+		cfg.Display.Input = abs
+	}
+	if cmd.Flags().Changed("rotate") {
+		cfg.Display.Rotate = rotate
+	}
+	if cmd.Flags().Changed("speed") {
+		cfg.Display.Speed = speed
+	}
+	if cmd.Flags().Changed("fps") {
+		cfg.Stream.FPS = fps
+	}
+	return nil
+}
+
+// resolveInput converts a relative path to an absolute one and verifies the
+// file exists, returning a helpful error otherwise.
+func resolveInput(input string) (string, error) {
+	abs, err := filepath.Abs(input)
+	if err != nil {
+		return "", fmt.Errorf("resolve input %q: %w", input, err)
+	}
+	if st, err := os.Stat(abs); err != nil {
+		return "", fmt.Errorf("input file %q does not exist", abs)
+	} else if st.IsDir() {
+		return "", fmt.Errorf("input %q is a directory, expected a media file", abs)
+	}
+	return abs, nil
+}