Store signal quality score in database for future analysis

- Add signalQualityScore field to Trade model (0-100)
- Calculate quality score in execute endpoint using same logic as check-risk
- Save score with every trade for correlation analysis
- Create database migration for new field
- Enables future analysis: score vs win rate, P&L, etc.

This allows data-driven decisions on dynamic position sizing

prisma/schema.prisma

@@ -75,6 +75,7 @@ model Trade {
   rsiAtEntry        Float?  // RSI momentum (0-100)
   volumeAtEntry     Float?  // Volume relative to MA
   pricePositionAtEntry Float? // Price position in range (0-100%)
+  signalQualityScore Int?   // Calculated quality score (0-100)
   fundingRateAtEntry Float? // Perp funding rate at entry
   basisAtEntry      Float?  // Perp-spot basis at entry