Add goreleaser config and version command for v0.1.0.

GoReleaser builds static binaries for linux/darwin on amd64/arm64,
injecting version via ldflags. Version command prints the embedded
version (defaults to "dev" for local builds).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/sgard/version.go

@@ -0,0 +1,21 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+var version = "dev"
+
+var versionCmd = &cobra.Command{
+	Use:   "version",
+	Short: "Print the version",
+	Run: func(cmd *cobra.Command, args []string) {
+		fmt.Println(version)
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(versionCmd)
+}