Adding AI Security Detections metrics to the Security Overview on the organisation level [Public Preview]

### Value Prop
Security managers and administrators can now see AI security detection findings, resolution rates, and feature impact across all their repositories directly in the Security Overview — no need to dig through individual pull requests. This org-level visibility makes it straightforward to measure whether AI-powered security detections are working and to share concrete results with security leadership. Teams get a clear picture of coverage and developer response in one place, making it easier to evaluate and expand their security programs.

### Expected Outcome
Adding these metrics to the Security Overview removes a key barrier for teams that have adopted AI security detections but lack a way to demonstrate their value internally. Security leaders and buyers gain the ROI visibility they need to make confident decisions about sustaining and scaling the feature across their organization. The goal is to help customers prove impact, support continued investment, and drive broader adoption of AI-powered security detection.

The issue names the organisation-level Security Overview and AI security detection metrics, but no files, tests, or entry points. Start by locating the Security Overview implementation and existing detection-metric aggregation. Done means the overview exposes findings, resolution rates, and feature impact across the organisation’s repositories.

Written by the indexing model from the issue text.