AI Security Detections on PRs [GA]

### Value Prop

Building on the Public Preview, the GA release of AI Security Detections on PRs delivers a polished experience for AI-powered security findings in pull requests.

### Expected Outcome

GitHub's AI security detections are now generally available, providing production-grade coverage for languages currently unsupported by CodeQL (PHP, Shell, HCL, JSP, Blazor), enabling security teams to enforce AI-found vulnerabilities as merge blockers, and delivering an improved developer experience with clearer alert presentation in pull requests.

No repository files, tests, or entry points are named in this roadmap issue, so begin by locating the implementation for AI security detections on pull requests. Done means delivering the GA experience, including coverage for PHP, Shell, HCL, JSP, and Blazor, merge-blocking security findings, and clearer pull-request alerts.

索引モデルが issue の本文から書いたものです。