Add Documentation checklist to PR template (#183)

- Add Documentation section with Architecture.md update requirement
- Helps ensure architecture documentation stays current with system changes

Co-authored-by: claude[bot] <209825114+claude[bot]@users.noreply.github.com>

Author: yangm2

.github/pull_request_template.md

@@ -36,4 +36,8 @@ images for UI changes._
       have not been included_
 - [ ] I need help with writing tests
 
+## Documentation
+
+- [ ] If this PR changes the system architecture, `Architecture.md` has been updated
+
 ## [optional] Are there any post deployment tasks we need to perform?