Add key price read model updated by indexer on each trade event

[Chucks1093]

Summary

The client currently has no fast path to get the current key price for a creator. Every price lookup either requires a direct Soroban RPC call or a round-trip that is too slow for a list view with many creators. The server needs a lightweight price read model that the indexer keeps current so the client can get prices with a single database read.

Scope

• Add a creator_price_snapshot table (or equivalent model) with fields: creator_id, current_price, price_24h_ago, last_trade_at, updated_at
• Update the indexer to write to this table whenever a buy or sell event is processed
• Expose current_price and price_change_24h fields on the creator detail and creator list responses
• Add an index on creator_id for fast lookups

Acceptance Criteria

• Price snapshot table exists and is seeded in development
• Indexer writes a new snapshot row (or updates in place) on every trade event
• Creator detail endpoint returns current_price and price_change_24h
• Creator list endpoint includes the same fields without extra per-row queries
• Integration test confirms price field updates after a simulated trade event

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