add goreleaser configuration for binaries and deb/rpm packages

- build static binaries for linux, darwin and freebsd
- create deb and rpm packages that register gosh in /etc/shells
- publish releases to Gitea
- add --version flag, set at build time via ldflags

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

main.go

@@ -19,6 +19,9 @@ import (
 // ErrNoPath is returned when 'cd' was called without a second argument.
 var ErrNoPath = errors.New("path required")
 
+// version is set at build time via -ldflags "-X main.version=..."
+var version = "dev"
+
 // previousDir tracks the previous working directory for 'cd -' support
 var previousDir string
 
@@ -483,6 +486,11 @@ func completeFilePath(line, prefix string) []string {
 }
 
 func main() {
+	if len(os.Args) > 1 && (os.Args[1] == "--version" || os.Args[1] == "-V") {
+		fmt.Println("gosh", version)
+		return
+	}
+
 	// Ctrl+C sends SIGINT to the whole foreground process group. Catch it so
 	// that it only stops the running command and not the shell. (signal.Ignore
 	// would be inherited by the child processes.)