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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ℹ️ Recent review info

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Reviewing files that changed from the base of the PR and between dab0a1b and 351cbf2.

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• .github/CONTRIBUTING.md

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🔇 Additional comments (1)

.github/CONTRIBUTING.md (1)

67-68: 🗄️ Data Integrity & Integration

Qualify the enforcement claims that the settings do not establish.

The active Require-Signed-Commits ruleset targets the default branch and contains required_signatures. However, the API does not establish zero bypass actors, and allow_rebase_merge is null. Remove or qualify the claim that rebase-merge is disabled until the repository setting is available.

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Added contribution guidance requiring signed commits on the default branch and specifying how people, agents, apps, bots and workflows should sign or push changes.
  • Clarified that pull requests must be squash-merged and that unsigned commits block merging.

Walkthrough

The contribution guide now sets out signing requirements for commits reaching the default branch. It also describes signing methods, PR branch requirements, and the squash-merge policy.

Changes

Commit-signing guidance

Layer / File(s)	Summary
Signing and merge requirements .github/CONTRIBUTING.md	The guide explains how people, interactive agents, apps, bots, and workflows must sign commits. It states that unsigned PR branch commits block merging, directs contributors to recreate such branches with signed cherry-picks, and specifies squash merging.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~3 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 351cb

The guide adds signed-commit and squash-merge instructions. No concrete mismatch or merge-blocking failure is established, so it appears ready for normal checks.

Architecture Summary

Architecture risk: 🔵 Low · up to 351cb

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: Added signing requirements for default-branch commits, with separate signing methods for people and interactive agents versus apps, bots and workflows. The guidance also specifies squash merges, explains that unsigned PR-branch commits block merging, directs contributors to recreate such branches with signed cherry-picks, and states that rebase-merge is disabled.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the documentation change to add a Signed commits section to CONTRIBUTING.
Description check	✅ Passed	The description is directly related to the documentation change and explains the signing policy guidance covered by the update.
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.

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_{A rabbit reads the signing guide,
Then signs each commit with care.
A squash-merge brings the branches close,
With verified email there.
The bunny hops away. 🐇}

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