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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• .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
  • Added guidance on commit-signing requirements for changes reaching the default branch, including how people, interactive agents, apps and workflows should create signed commits.
  • Clarified that unsigned pushes are rejected, every commit on a pull request branch is checked, and squash merges are required. Branches containing unsigned commits must be recreated with signed commits, and rebase merges are disabled.

Walkthrough

The contribution guide adds signed-commit requirements and instructions for people and automated processes. It also explains pull request commit checks and merge rules.

Changes

Commit guidance

Layer / File(s)	Summary
Signed commit instructions .github/CONTRIBUTING.md	The guide specifies SSH signing for people and interactive agents, and GitHub API or signed-push action commits for apps, bots and workflows. It requires squash merges, explains that every pull request branch commit is checked, and instructs contributors to recreate branches that contain unsigned commits.

Priority: ⬇️ Low

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

Change: Other

Merge Risk: ⚪ Minimal · up to 49b61

This change documents signed-commit and squash-merge expectations. The available evidence supports the PR-branch signature requirement; no actionable merge-blocking issue was established.

Architecture Summary

Architecture risk: 🔵 Low · up to 49b61

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 signing instructions for people, interactive agents, apps, bots and workflows. It specifies squash merges, explains that every PR-branch commit is checked and unsigned commits block merging, instructs contributors to recreate unsigned branches with signed commits, 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 main change: adding a Signed commits section to CONTRIBUTING.
Description check	✅ Passed	The description directly explains the documentation change, its signing policy, and the related contributor requirements.
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 a commit with care,
Then hops through checks without a scare.
Squash the branch and make it neat,
Signed commits keep the rules complete.
The guide now shows the way to go.}

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

✨ Finishing Touches 💡 1

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