docs: add public pull request disclosure safeguards

[kmbroai]

Summary

Help contributors and agents prepare clear public pull requests without disclosing confidential or identifying information.

Changes

• Add a default pull request template with summary, changes, testing, risk, and disclosure-review sections.
• Add matching agent instructions for branch names, commit messages, generated content, and pull requests.

Testing

• Targeted Prettier formatting checks passed for both changed files.
• git diff --check passed.
• Confirmed the change contains only AGENTS.md and the pull request template.

Risk and rollout

Low risk: agent guidance and GitHub's default pull request template only. No runtime, contributor-guideline, or workflow changes.

Public disclosure review

• No customer, partner, prospect, or user identities, data, or identifying details are included.
• No credentials, personal data, private source, scan findings, or nonpublic links or tickets are included.
• I reviewed the branch name, title, description, commits, changes, comments, logs, screenshots, attachments, and links for public disclosure.