docs: add PR template convention to AGENTS.md

[avoidwork]

Summary

• Adds .github/PULL_REQUEST_TEMPLATE.md for structured PR descriptions
• Documents the template convention in AGENTS.md section 7.4

Files Changed

• .github/PULL_REQUEST_TEMPLATE.md — New PR template (Type of Change, Related Issues, Testing, Checklist)
• AGENTS.md — Section 7.4: Pull Request Templates convention

Checklist

• npm test passes
• npm run build succeeds
• No hardcoded secrets or credentials introduced
• Zero external dependencies added

[augmentcode]

🤖 Augment PR Summary

Summary: Adds a new Git Conventions subsection documenting the required use of the repository’s PR template when present.
Changes: Appends section 7.4 Pull Request Templates to AGENTS.md to require completing all template sections (using N/A when not applicable).

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[augmentcode]

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