Document required code owner review gate

[Will-thom]

Summary

• Document required pull request review and code owner review as active branch-protection guardrails.
• Document the temporary founder bypass needed while Will-thom is the only maintainer and code owner.
• Update maintainer, CI, OSS guardrail, and permission posture docs.

Validation

• Documentation-only change.

Follow-up after merge:

• Enable required pull request review and code owner review on main.

[github-actions]

Hi @Will-thom, thank you for contributing to PR Maven CLI.

I appreciate the time you spent opening this pull request. This project is intentionally shaped for focused, reviewable open source contributions, so your input helps the tool become more useful for Java and Maven teams.

A maintainer will review the context, labels, and next steps as soon as possible. If this is your first contribution here, welcome aboard.

Useful links:

• Contributing guide: CONTRIBUTING.md
• Testing guide: docs/testing.md
• CI/CD guide: docs/ci.md

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