Enforce issue pull request and commit conventions

[bmuddha]

Outcome

Enforce consistent issue, pull request, and commit conventions in Engine.

Scope

Port MBV’s conventions workflows and required-field issue forms, including rejection of formatting-only answers. Leave runtime code unchanged.

Acceptance criteria

• PR titles and non-merge commit subjects follow the repository’s Conventional Commit format.
• Issue titles and required template sections are validated, with invalid issues labeled needs-template-fix.
• Correcting an issue removes the label; formatting-only answers remain invalid.