feat: Add 'eko version' command with runtime & git commit details

[kavix]

🎯 Goal

Implement an eko version subcommand (and -v / --version flag on the root command) that prints CLI version details, Go runtime version, target OS/Arch, and Git commit hash.

💡 Expected Usage

$ eko version
eko version 1.1.0 (darwin/arm64)
Go version: go1.22.0
Git commit: 8c9d1a2f

🛠️ Implementation Steps

1. Create cmd/version.go defining Cobra command versionCmd.
2. Add global variables Version, Commit, BuildDate set via -ldflags during build.
3. Wire -v / --version flag into cmd/root.go.
4. Add unit test in cmd/commands_test.go.

[vsolano9]

I'll take this. I'll implement both the subcommand and root flags, wire release metadata through GoReleaser, add regression coverage for the rendered fields and aliases, and document the command.