Add --version / version with baked-in git commit

ldflags inject version, commit, and build date; a version subcommand
also reports go version and platform. Ends the which-binary-is-this
guessing after deploys.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/rtsp-streamer/commands.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"os/signal"
+	"runtime"
 	"sort"
 	"syscall"
 	"text/tabwriter"
@@ -17,6 +18,21 @@ import (
 	"github.com/spf13/cobra"
 )
 
+// versionCmd prints detailed build and runtime info.
+func versionCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:   "version",
+		Short: "Print version, git commit, and build info",
+		Run: func(cmd *cobra.Command, _ []string) {
+			fmt.Printf("rtsp-streamer %s\n", version)
+			fmt.Printf("  commit:   %s\n", commit)
+			fmt.Printf("  built:    %s\n", date)
+			fmt.Printf("  go:       %s\n", runtime.Version())
+			fmt.Printf("  platform: %s/%s\n", runtime.GOOS, runtime.GOARCH)
+		},
+	}
+}
+
 // daemonCmd runs the video wall. This is what systemd (via sway) launches.
 func daemonCmd() *cobra.Command {
 	return &cobra.Command{