Add checklist finalisation workflow for closed issues and merged PRs

[ashleyshaw]

Summary

Add an automated backstop that rewrites checklist sections in closed issue bodies and merged PR descriptions so the final state reflects completion instead of leaving stale unchecked boxes behind.

Problem

The current template enforcement workflow validates issue and PR checklists, but it does not rewrite the body when an issue is closed or a PR is merged. That leaves the description inconsistent with the final state and makes completed items look incomplete.

Proposed Fix

• Add a workflow that triggers on closed issues and merged PRs.
• Update the body checklist sections so completed items are marked as checked.
• Keep the existing validation workflow strict so incomplete bodies still fail before merge or close.
• Document the finalisation path for maintainers and automation callers.

Acceptance Criteria

• Closed issues have their DoR/DoD checklist sections rewritten to reflect completion.
• Merged PRs have their checklist section rewritten to reflect completion.
• The validation workflow still blocks incomplete issue/PR bodies.
• Documentation mentions the finalisation workflow.
• The workflow YAML parses cleanly.

Definition of Ready (DoR)

• The terminal states for issues and PRs are identified.
• The checklist section headings are known.
• The workflow trigger events are confirmed.

Definition of Done (DoD)

• Workflow added.
• Documentation updated.
• Validation completed.
• The repository's live issue/PR descriptions reflect the finalised state where applicable.

References

• .github/workflows/template-enforcement.yml
• .github/pull_request_template.md
• .github/ISSUE_TEMPLATE/
• docs/PR_CREATION_PROCESS.md
• docs/WORKFLOW_COORDINATION.md

[linear-code]

LS-994

LS-1110