chore(dependabot): cap open pull requests per update block

[hyperpolymath]

Adds open-pull-requests-limit to Dependabot update blocks that had no cap, following the estate per-ecosystem cap doctrine (task #37). No other line in the file is touched.

Claude-Session: https://claude.ai/code/session_011eQ7hibx92N7fBDtwgReWk

Summary

Closes #

Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (would change existing behaviour)
• 🕳️ Soundness fix (fixes a checker/proof false-negative)
• 📖 Documentation
• 🧹 Refactor / tech debt (behaviour-preserving)
• ⚡ Performance
• 🔧 Build / CI / tooling

How has this been verified?

Checklist

• My commits are signed (git commit -S).
• I ran the project's own checks/tests locally and they pass.
• New files carry the correct SPDX-License-Identifier (code/config MPL-2.0,
  prose CC-BY-SA-4.0); I did not relicense existing files.
• Docs are updated, and no public claim now overstates what the code does.
• I have not introduced a soundness hole (or I have flagged where I might have).

Notes for reviewers

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 2ba99a3c-71dd-4353-acd5-9f6609a6631f

📥 Commits

Reviewing files that changed from the base of the PR and between b9eb7e1 and 350420d.

📒 Files selected for processing (1)

• .github/dependabot.yml

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📝 Summary

Summary by CodeRabbit

• Chores
  • Limited the number of simultaneous automated dependency update pull requests across GitHub Actions, Mix, npm and pip.
  • Updated documentation explaining the Cargo update limit with a reference to the relevant audit information.

Walkthrough

The Dependabot configuration now limits open pull requests for GitHub Actions, Mix, npm, and pip. The Cargo explanation comment now references a commit and audit report.

Changes

Dependabot configuration

Layer / File(s)	Summary
Configure ecosystem pull request limits .github/dependabot.yml	GitHub Actions has an open pull request limit of 2. Mix, npm, and pip have a limit of 3. The Cargo comment now references a commit and audit report.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Change: Other

Suggested reviewers: metadatastician

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

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_{A rabbit checks the update queue
Two hops here, and three hops there
Dependabot keeps the paths in line
Cargo’s note points to its record
The burrow stays neatly ordered}

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

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud