Establish controlled promotion policy

[mayankhansraj12]

Production promotion

This pull request promotes the reviewed and CI-validated dev state to main.

Included controls

• main accepts pull requests only from this repository dev branch
• dev accepts normal contributor pull requests
• both long-lived branches run the same core CI pipeline
• Dependabot targets dev
• governance and authenticated audits enforce the policy

Verification

• feature PR Enforce controlled dev-to-main promotion #12 passed Build, test, and package
• local validation passed 107 tests
• workflow lint and YAML validation passed