fix: restrict github repo monitor triggers by login

[enyst]

Summary

• Adds ALLOWED_GITHUB_LOGINS to the GitHub repo monitor script, defaulting to the authenticated GITHUB_TOKEN owner.
• Skips trigger comments from unauthorized GitHub logins before creating, resuming, or forwarding to conversations.
• Updates the skill setup workflow and README to ask who may trigger the automation.
• Adds unit coverage for token-owner, explicit allowlist, wildcard, and missing-author behavior.

Validation

• uv run pytest -q
• uv run python scripts/sync_extensions.py --check

This PR was created by an AI agent (OpenHands) on behalf of the requester.

@enyst can click here to continue refining the PR

[all-hands-bot]

🟢 Good taste - Clean security improvement with secure defaults.

VERDICT: ✅ Worth merging - Adds access control for automation triggers with comprehensive tests and clear documentation.

KEY INSIGHT: Elegant security-by-default design using token-owner sentinel that resolves at runtime, preventing unauthorized trigger abuse while maintaining flexibility through explicit allowlists.

[RISK ASSESSMENT]

• [Overall PR] ⚠️ Risk Assessment: 🟢 LOW

Security improvement that adds access control for GitHub repo monitor triggers. Clean implementation with secure defaults (token owner only), comprehensive test coverage, and no breaking changes to existing deployments. The bot check before auth check correctly prevents bot loops. The conditional logging provides useful security audit information without log spam.

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Workflow run: https://github.com/OpenHands/extensions/actions/runs/26334073422