chore: import upstream snapshot with attribution

.github/PULL_REQUEST_TEMPLATE.md

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+## Summary
+
+Brief description of what this PR does.
+
+## Type of Change
+
+- [ ] New agent
+- [ ] New skill
+- [ ] New hook or rule
+- [ ] Bug fix
+- [ ] Documentation improvement
+- [ ] Other:
+
+## Changes
+
+-
+-
+-
+
+## Checklist
+
+- [ ] I've tested this in a Claude Code session
+- [ ] New agents include the Collaboration Protocol section
+- [ ] New skills use the subdirectory format (`.claude/skills/<name>/SKILL.md`)
+- [ ] Reference docs are updated (agent-roster, skills-reference, hooks-reference, rules-reference)
+- [ ] Hooks use `grep -E` (POSIX) and fail gracefully without jq/python
+- [ ] No hardcoded paths or platform-specific assumptions