pull_request_template.md

What & why

Type

• New extension
• Fix / improvement to an existing extension
• Tooling / CI / docs

Checklist

• node scripts/lint.mjs passes
• node scripts/validate-extensions.mjs passes
• node scripts/run-tests.mjs passes
• New/changed extension has a smoke test under extensions/<name>/test/
• README extensions table updated (when adding or removing an extension)