Agentic autofix generation for code scanning alerts [GA]

### Value Prop
With agentic autofix for code scanning alerts, users can automatically resolve security issues in their code by assigning alerts to an advanced agent that generates and submits pull requests with fixes. This streamlines the remediation process, saving time and reducing manual effort for development and security teams.

### Expected Outcome
By making agentic autofix generally available to all paying GitHub Advanced Security and code security users, more organizations can quickly address vulnerabilities and maintain secure codebases. The goal is to increase the speed and efficiency of fixing code scanning alerts, leading to stronger security and less operational overhead.

路线图条目描述了针对 code scanning 警报的 agentic autofix，但没有指出任何仓库文件、测试或实现入口。首先明确面向 GitHub Advanced Security 和 code security 付费用户的一般可用范围与验收标准；完成意味着所述的 autofix 功能已正式全面可用。

由索引模型根据 Issue 内容生成。