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)

92-93: 🎯 Functional Correctness

Do not state that rebase merging is disabled without a repository setting that supports it.

The active Require-Signed-Commits ruleset targets ~DEFAULT_BRANCH. However, the repository API returned null for allow_rebase_merge and allow_squash_merge, so the claim that rebase merging is disabled remains undecided. The guidance should retain that statement only if an authoritative setting confirms it.

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📝 Summary

Summary by CodeRabbit

• Documentation
  • Added contribution guidance on commit signing, including requirements for contributors and automated workflows.
  • Clarified that unsigned commits must be replaced before merging and that squash merging is used.

Walkthrough

The contribution guide now requires signed commits to reach the default branch. It gives signing instructions for people, interactive agents, apps, bots and workflows. It also specifies squash merging and states that rebase merging is disabled.

Changes

Signed commit guidance

Layer / File(s)	Summary
Signing and merge instructions .github/CONTRIBUTING.md	Adds signing requirements and separate procedures for people and interactive agents, and for apps, bots and workflows. Directs contributors to squash-merge, states that unsigned pull request commits block merging, and notes that rebase merging is disabled.

Priority: ⬇️ Low

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

Change: Other

Merge Risk: ⚪ Minimal · up to 44f29

The confirmed repository settings match the key signing and merge guidance; no actionable issue is established.

Architecture Summary

Architecture risk: 🔵 Low · up to 44f29

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 guidance requiring signed commits on the default branch, with separate signing procedures for people and interactive agents versus apps, bots and workflows. It directs contributors to squash-merge; unsigned commits on a PR branch block merging, and 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 and its commit-signing 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 each change with care,
Then checks the merge rules waiting there.
SSH keys for people shine,
API commits suit bots in line.
Squash the branch; the guide is clear,
And hop to merge with signed commits here.}

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