Simplify pull_request_template.md

[JimmyShi22]

Currently pull_request_template.md is very complicated and it hard for us to use it. Please rewrite it according with the historical PR in this repo.

[JimmyShi22]

@claude please help

[github-actions]

Claude finished @JimmyShi22's task in 1m 1s —— View job • claude/issue-231-20260326-1104 • Create PR ➔

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Simplifying pull_request_template.md

• Gather context
• Read current template and historical PRs
• Rewrite the template
• Commit and push changes

The PR template has been simplified. Here's what changed:

Removed:

• The entire "Code Guidelines" section with 6+ doc links
• Verbose comments on each section
• Extra checklist items (self-comments, hard-to-understand areas)
• "Additional Notes" and "Testing" free-form sections

Kept (minimal):

• Description
• Type of Change checkboxes
• A 3-item checklist: just check, self-review, tests

New template:

## Description


## Type of Change
- [ ] Bug fix
- [ ] New feature
- [ ] Breaking change
- [ ] Refactoring
- [ ] Documentation update
- [ ] Other

## Checklist
- [ ] Code passes `just check` (format, clippy, tests)
- [ ] Self-review completed
- [ ] Tests added or updated if needed