refactor: use Go native build info for commit and date

[fank]

Summary

• Replace ldflags injection of commit and date with runtime/debug.ReadBuildInfo() which Go embeds automatically from VCS
• Only version remains as an ldflag (no native way to get the git tag at runtime)
• Aligns the build pattern across all three CLIs (esq, atl, n8nctl) to use identical ldflags: -X main.version={{.Version}}

Test plan

• go vet ./... passes
• Local build shows correct commit hash and build date from VCS
• Version injection via ldflag still works: go build -ldflags "-s -w -X main.version=1.2.0"
• -s -w stripping does NOT affect runtime/debug build info

[gemini-code-assist]

Code Review

This pull request refactors the versioning system to retrieve VCS information at runtime using the runtime/debug package instead of relying on build-time ldflags. The vcsInfo function was introduced to extract the commit hash and build date directly from the binary's build info. Feedback suggests enhancing this function to check the vcs.modified flag, which would allow the version output to indicate if the binary was built from a repository with uncommitted changes.