[frontend] Fix PriceChart REST and WebSocket protocol mismatch with API

[Mimah97]

Problem

Three protocol mismatches break live price charts:

1. usePriceCandles expects { candles: [] }; API returns a raw array
2. WebSocket sends { event: "subscribe_candles", ... }; gateway expects { action: "subscribe", poolId }
3. Candle field names differ (time vs timestamp)

Acceptance criteria

• Align subscription protocol between frontend and PriceGateway
• Normalize response DTO in PriceController
• PriceChart renders real aggregated candles

Files

• apps/api/src/price/price.gateway.ts
• apps/web/hooks/usePriceCandles.ts