chore: adopt org-infra reusable CI workflows (MegaLinter, PR title checks)

[jflowers]

Summary

Adopt the complytime/org-infra reusable CI workflows for standardized linting and PR title validation.

Context

The canonical reference (unbound-force/unbound-force/.github/workflows/ci_checks.yml) calls a reusable workflow from complytime/org-infra that runs MegaLinter and PR title convention checks. Replicator currently has no equivalent — it only runs go vet and go test.

Adopting the org-infra workflows would:

• Add MegaLinter (multi-language linting including YAML, Markdown, shell scripts)
• Add PR title validation (Conventional Commits enforcement)
• Align with the standardized CI check names the release preflight expects (Standardized CI / Run linters)

Acceptance Criteria

• Add ci_checks.yml calling the org-infra reusable workflow
• MegaLinter runs on PRs and push to main
• PR title validation enforces Conventional Commits format
• Update release preflight to also verify Standardized CI / Run linters passed (once available)

References

• Parent issue: chore: add CI gate before release + pin action versions to commit SHAs #15 (out of scope item)
• Canonical reference: unbound-force/unbound-force/.github/workflows/ci_checks.yml
• Org-infra reusable workflows: complytime/org-infra