Evaluation: Display overall score summary

[AkhileshNegi]

Is your feature request related to a problem?
v2 runs include score.overall and an ai_summary for identifying the weakest questions, but these are not displayed on the run detail page. This makes it difficult for users to quickly assess the overall performance of their runs.

Describe the solution you'd like

• Display score.overall at the top of the run detail page, including overall_score, verdict, and breakdown (score, weight, delta, verdict)
• Show ai_summary as a diagnostic note above the per-row table
• Ensure graceful degradation when ai_summary is null or when overall is absent on v1 runs

Original issue

Is your feature request related to a problem?
v2 runs carry score.overall — a weighted rollup across the judge metrics plus a natural-language ai_summary pointing at the worst questions. Today the run detail page shows neither, so the reader has to eyeball three metrics and every row to work out how the run went.

Describe the solution you'd like

• Render score.overall at the top of the run detail page: overall_score, verdict, and the per-metric breakdown (score, weight, delta, verdict)
• Render ai_summary as a diagnostic note above the per-row table
• Degrade gracefully when ai_summary is null (best-effort, never fails the run) or when overall is absent on v1 runs

Parent: #265