feat(33-01): add market_prices, community_prices tables and currency columns
- Add marketPrices table with unique(globalItemId, market, currency) constraint
- Add communityPrices table with unique(globalItemId, userId, sourceType) constraint
- Add priceCurrency column to items table (default EUR)
- Add foundPriceCents, foundPriceCurrency, foundPriceDate to threadCandidates
- Add Zod schemas for market price upsert and community price submission
- Export new types from shared/types.ts
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>