feat: Sprint 7.4 — model intelligence dashboard

[justn-hyeok]

Summary

• Thompson Sampling visualization: model leaderboard, quality trends, selection frequency, provider reliability
• New components: ModelLeaderboard, QualityTrend, SelectionFrequency, ProviderReliability
• Pure utility functions in model-helpers.ts
• 21 new tests

Features

• Ranked leaderboard table with win rates, confidence intervals, color-coded performance
• SVG line chart showing compositeQ trends per model over time
• Selection frequency bar chart grouped by model
• Provider reliability cards with health status (healthy/degraded/unhealthy)

Test Plan

• 21 new tests — all pass
• computeWinRate, computeConfidenceInterval, groupByProvider, aggregateHistory, getQualityTrend

Sprint 7 Feature 5.4 / 8

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