Elevate Attestation as a First-Class Object in Repository UI and Security Overview [Public Preview]

### Value Prop
You can now easily view and verify attestations directly in your repository’s UI and Security Overview, with clear SLSA level indicators. This makes it simpler for developers, security admins, and compliance leads to assess trust and compliance at a glance, streamlining your security workflows.

### Expected Outcome
By making attestations a first-class part of the repository experience, we aim to reduce friction and increase adoption of secure development practices. This change helps enterprise teams meet SLSA source track requirements and strengthens trust in your software supply chain.

roadmap issue 未指出任何文件、测试或入口点。将预期结果作为起始规范：确定 attestations 应如何在 repository UI 和 Security Overview 中呈现和验证，包括清晰的 SLSA 级别指标。当这些界面支持所述的 attestation 及信任/合规工作流时，即表示完成。

由索引模型根据 Issue 内容生成。