feat(data-api): chain sub-scores in By Provider pivot

[Flotapponnier]

Summary

• Adds DataApiChainScore type and chains? field on DataApiProviderCell
• computeProviderChainScores() checks bestPerChain — if a provider is the winner on a chain, that chain appears as a colored chip
• Region + chain sub-scores merged into one flex-wrap row in GroupCell (no separate sections)
• ChainSubScores renders compact accent-colored chips (e.g. Base, ETH, SOL) capped at 4 + overflow count