docs: add Signed commits section to CONTRIBUTING

[hyperpolymath]

Adds a Signed commits section to this repo's CONTRIBUTING, per owner ruling D218. The estate policy is docs/SIGNING-POLICY.adoc in hyperpolymath/standards.

This repo's default branch is covered by the zero-bypass Require-Signed-Commits ruleset, and rebase-merge is off. The section tells contributors what that requires:

• People and interactive agents sign with an SSH signing key.
• Apps, bots and workflows write through the API, so GitHub signs their commits.
• PRs are merged with squash.

If the file already had its own signing section, that section is replaced in place instead of adding a second one. Lines elsewhere that told people to sign with GPG are changed to match the policy (SSH for people).

This is a docs-only change. The commit was created through createCommitOnBranch, so GitHub signs it.

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• .github/CONTRIBUTING.md

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🔇 Additional comments (1)

.github/CONTRIBUTING.md (1)

123-138: LGTM!

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Updated the contributing guide with commit-signing requirements, guidance for people and automated workflows, and details on merge restrictions.

Walkthrough

The contributing guide now sets out signed-commit requirements, signing methods for different commit authors, and merge rules for pull requests.

Changes

Contribution Guidance

Layer / File(s)	Summary
Signed commit requirements .github/CONTRIBUTING.md	The guide requires signed commits and describes signing methods for people, interactive agents, apps, bots, and workflows. It specifies squash merges and explains that unsigned pull request commits block merging; rebase merging is disabled.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~8 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 5fd13

The signing instructions match the estate policy and merge restrictions. No concrete documentation risk remains, so the change is ready to merge.

Architecture Summary

Architecture risk: 🔵 Low · up to 5fd13

The changed surface does not map to a changed system, dependency edge, entrypoint, or external dependency.

Changed systems: None identified.

Architecture concerns
No architecture-level concerns identified.

Review details

Before / after behavior

• observed — Modified behavior in .github/CONTRIBUTING.md: Adds signed-commit requirements and instructions for people, interactive agents, apps, bots and workflows, including SSH signing configuration, API-based commit creation, squash merging, and handling unsigned PR commits; states that rebase-merge is disabled.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the purpose and main changes, but it does not follow the required template. It omits the Summary, Changes, RSR Quality Checklist, Testing, and Screenshots sections, including …	Add all required template sections. List the key changes, mark each applicable checklist item, describe the testing performed, and add screenshots or terminal output when applicable.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the documentation change: adding a Signed commits section to CONTRIBUTING.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description explains the purpose and main changes, but it does not follow the required template. It omits the Summary, Changes, RSR Quality Checklist, Testing, and Screenshots sections, including the required checklist status and testing information.

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_{A rabbit signs a commit with care,
Then checks the merge rules waiting there.
SSH keys make the record clear,
Squash the branch when merges draw near.
The guide now tells the steps to do,
And keeps each unsigned commit in view.}

_{Comment @coderabbitai help to get the list of available commands.}