Enforce pull request, commit, and issue conventions

[bmuddha]

Outcome

Pull request titles, commit subjects, and issues follow the repository conventions automatically.

Scope

Add PR-only title and non-merge commit validation. Convert the four issue templates to required forms and flag malformed issue titles or sections with a removable needs-template-fix label. Align generated release titles with the same commit format.

Acceptance criteria

• PR title edits and new commits rerun the convention check; merge commits are exempt.
• All existing issue sections are required in the forms, and issues created or edited through CLI/API are checked too.
• Corrected issues lose the validation label without comments, closure, or content rewrites.
• Release-generated PR and commit titles conform; direct pushes and branch protection remain unchanged.