docs: enhance release flow documentation and add version command to CLI

- Updated AGENTS.md and README.md to clarify the automated release process using release-please and GoReleaser.
- Added a version command to the envc CLI to display build metadata.
- Included CI/CD details in README for better understanding of testing and release automation.

cmd/envc/main.go

@@ -5,11 +5,19 @@ import (
 	"os"
 )
 
+// Build metadata injected at release time via -ldflags.
+// Defaults keep local `go build` / `go install` builds identifiable as unversioned.
+var (
+	version = "dev"
+	commit  = "none"
+	date    = "unknown"
+)
+
 func main() {
 	stdin, stdout, stderr := os.Stdin, os.Stdout, os.Stderr
 	args := os.Args[1:]
 	if len(args) < 1 {
-		_, _ = fmt.Fprintln(stderr, "usage: envc <convert|get|merge> [flags]")
+		_, _ = fmt.Fprintln(stderr, "usage: envc <convert|get|merge|version> [flags]")
 		os.Exit(2)
 	}
 	var code int
@@ -20,6 +28,8 @@ func main() {
 		code = RunGet(args[1:], stdin, stdout, stderr)
 	case "merge":
 		code = RunMerge(args[1:], stdin, stdout, stderr)
+	case "version", "--version", "-v":
+		_, _ = fmt.Fprintf(stdout, "envc %s (commit %s, built %s)\n", version, commit, date)
 	default:
 		_, _ = fmt.Fprintf(stderr, "unknown command %q\n", args[0])
 		code = 2