Improve PR compliance workflow feedback and enforcement

### Description

Update the compliance workflow so that pull requests with a missing or invalid closing issue reference are clearly guided to fix the PR description and remain blocked by a required failing check until compliant. Use one maintained bot comment for feedback; do not add an automated review or auto-assign the PR author.

### Action Items

- [ ] Review the current linked-issue validation and branch-protection requirements.
- [ ] Validate closing references against repository issues and reject pull request references.
- [ ] Make the compliance job fail while the PR is missing or has an invalid closing issue reference.
- [ ] Create or update one bot comment, identified by a stable marker, with the exact remediation guidance.
- [ ] Update the maintained comment to confirm the valid linked issue once compliant.
- [ ] Prevent duplicate comments on synchronize and other repeat events.
- [ ] Handle an empty PR body and await all API calls.
- [ ] Remove unnecessary checkout and minimize workflow permissions and triggers.
- [ ] Update the pull request template so Related Issues has an empty input and retains `Resolves #123` only as a commented example.
- [ ] Align Related Issues guidance in the PR template with the maintained compliance-bot comment.
- [ ] Add or update tests/documentation for the workflow behavior.

### Additional Information

Selected approach: required failing compliance check plus one maintained bot comment.

Out of scope: automated PR review comments and automatically assigning the PR author.

The maintained comment should tell the contributor exactly how to add a valid closing reference, such as `Resolves #123`, in Related Issues, then confirm the linked issue when compliant.

The PR template must not render the literal `Resolves #ISSUE_NUMBER` placeholder; retain `Resolves #123` only as an HTML-comment example, and use wording that matches the maintained bot comment.