docs: add PR template and AGENTS.md section 5.4

[avoidwork]

Summary

• Added .github/PULL_REQUEST_TEMPLATE.md for structured PR descriptions
• Added section 5.4 Pull Request Templates to AGENTS.md

Changes

• New PR template with checklists aligned to project conventions (lint, coverage, forbidden patterns, conventional commits)
• AGENTS.md updated with section 5.4 per project guidelines

Testing

• N/A

Coverage

• N/A

Related Issues

• N/A

[augmentcode]

🤖 Augment PR Summary

Summary: Adds a standardized pull request template and documents that it is mandatory for this repository.

Changes:

• Introduces .github/PULL_REQUEST_TEMPLATE.md with structured sections for description, change type, testing, coverage, and a PR checklist.
• Updates AGENTS.md with a new “5.4 Pull Request Templates” rule requiring the template be used and all sections completed (use N/A when not applicable).

Technical Notes: No runtime/code changes; this is process/documentation only.

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[augmentcode]

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