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>

Makefile

@@ -1,7 +1,15 @@
 BINARY := rtsp-streamer
 PKG := ./cmd/rtsp-streamer
 BINDIR := bin
-LDFLAGS := -s -w
+
+# Build metadata baked into the binary (see `rtsp-streamer version`).
+VERSION ?= $(shell git describe --tags --always --dirty 2>/dev/null || echo dev)
+COMMIT  ?= $(shell git rev-parse --short HEAD 2>/dev/null || echo none)
+DATE    ?= $(shell date -u +%Y-%m-%dT%H:%M:%SZ)
+LDFLAGS := -s -w \
+	-X main.version=$(VERSION) \
+	-X main.commit=$(COMMIT) \
+	-X main.date=$(DATE)
 
 # Install location. Override with `make install PREFIX=/opt`.
 PREFIX ?= /usr/local

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{

cmd/rtsp-streamer/main.go

@@ -17,10 +17,18 @@ var (
 	logLevel string
 )
 
+// Build metadata, injected via -ldflags -X at build time (see Makefile).
+var (
+	version = "dev"
+	commit  = "none"
+	date    = "unknown"
+)
+
 func main() {
 	root := &cobra.Command{
 		Use:           "rtsp-streamer",
 		Short:         "Full-screen RTSP camera wall for UniFi Protect",
+		Version:       fmt.Sprintf("%s (commit %s, built %s)", version, commit, date),
 		SilenceUsage:  true,
 		SilenceErrors: true,
 	}
@@ -34,6 +42,7 @@ func main() {
 		statusCmd(),
 		tuiCmd(),
 		configCmd(),
+		versionCmd(),
 	)
 
 	if err := root.Execute(); err != nil {