Add get_github_advisory tool to view GHSA details #3546

Describe the feature or problem you’d like to solve

Agents sometimes (always?) fail to retrieve the contents of GitHub Security Advisories (GHSAs), which forces them to rely on inaccurate secondhand sources. No one in their right mind wants to sit down and carefully read through the GHSAs that affect their projects, so if at all possible, I'd rather have an agent do the legwork: assessing the impact, researching workarounds, and so on.

Proposed solution

Add get_github_advisory tool. Given a GHSA ID or a CVE ID, return the same content we humans see in the browser. For example, given "GHSA-w3rx-r6r6-pgpr" or "CVE-2025-71330", return the contents of GHSA-w3rx-r6r6-pgpr.

Example prompts or workflows (for tools/toolsets only)

• Does GHSA-xxxx-xxxx-xxxx affect on this project?
• Are there any GHSAs that have not been fixed in the latest (backported to this major) version?
• How can malicious users pwn the server misusing GHSA-xxxx-xxxx-xxxx?
• Has GHSA-xxxx-xxxx-xxxx been patched in the latest version?
• Explain each vulnerability existing in depending packages in this project.

Additional context