[TypeSpec Authoring][Benchmark] Integrate Vally dashboard into SDK framework

[haolingdong-msft]

Parent epic: #15726

Integrate the Vally dashboard into the SDK framework so benchmark results (pass-rate trends, per-run timing, per-category breakdowns) are surfaced within our existing SDK tooling/reporting rather than viewed in isolation.

Scope

• Wire the Vally dashboard/reporting output into the SDK framework's reporting surface.
• Ensure per-run timing, pass-rate trends, and per-category breakdowns are visible.
• Make the dashboard accessible from the standard benchmark pipeline outputs.

Created as a sub-issue of the "[Epic][TypeSpec Authoring][Benchmark] Continuous improvement" epic (#15726), under its "Strengthen reporting and dashboards" scope item.

[helen229]

Cross-epic dependency for the evaluation framework epic #16344. This issue intentionally remains under TypeSpec Authoring epic #15726. For the shared framework, coordinate dashboard integration with the normalized Kusto work in #16350 and AI trend reporting in #16351.

[helen229]

Meeting update (2026-07-17): dashboard integration is the next major reporting task after the pipeline/tools-repo foundation. Effort estimate should follow the stable result schema/Kusto ingestion assessment in #16350, including whether existing Pipeline Witness ingestion/reporting can be reused. Keep this issue as the dashboard implementation tracker rather than filing a duplicate under #16344.