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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🔇 Additional comments (1)

.github/CONTRIBUTING.md (1)

123-138: LGTM!

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Updated contribution guidance to require signed commits on the default branch. People and interactive agents must use a registered SSH signing key and verified committer email; apps, bots and workflows must use the approved API or signed-push action.
  • Pull requests must be squash-merged. Unsigned commits prevent merging, and rebase merging is no longer available.

Walkthrough

The contribution guidance now specifies signed-commit requirements, signing methods for different contributors, and pull request merge rules.

Changes

Contribution rules

Layer / File(s)	Summary
Commit signing and merge rules .github/CONTRIBUTING.md	The guidance specifies signing requirements for people, interactive agents, apps, bots and workflows. It states that unsigned commits block merging, pull requests must be squash-merged, and rebase merging is disabled.

Priority: ⬇️ Low

Estimated code review effort: 1 (Trivial) | ~4 minutes

Change: Other

Merge Risk: ⚪ Minimal · up to 7dc61

The signed-commit and squash-merge guidance is consistent with the repository’s rules; no material merge risk remains.

Architecture Summary

Architecture risk: 🔵 Low · up to 7dc61

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 contribution guidance requiring signed commits on the default branch, specifying SSH signing and verified-email requirements for people and interactive agents, API-based commit creation for apps, bots and workflows, and squash merges. Unsigned PR commits block merging; 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 changeset and explains the signed-commit policy, contributor requirements, and documentation scope.
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 signs each commit with care
Then checks the merge rules in the air
Squash the branch, the guide says so
Unsigned commits cannot go
The rabbit hops, its work is done}

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✨ Finishing Touches 💡 1

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