feat: Add phantom trade detection and database tracking

- Detect position size mismatches (>50% variance) after opening
- Save phantom trades to database with expectedSizeUSD, actualSizeUSD, phantomReason
- Return error from execute endpoint to prevent Position Manager tracking
- Add comprehensive documentation of phantom trade issue and solution
- Enable data collection for pattern analysis and future optimization

Fixes oracle price lag issue during volatile markets where transactions
confirm but positions don't actually open at expected size.

lib/drift/orders.ts

@@ -29,6 +29,8 @@ export interface OpenPositionResult {
   fillSize?: number
   slippage?: number
   error?: string
+  isPhantom?: boolean // Position opened but size mismatch detected
+  actualSizeUSD?: number // Actual position size if different from requested
 }
 
 export interface ClosePositionParams {
@@ -179,16 +181,37 @@ export async function openPosition(
       const fillPrice = position.entryPrice
       const slippage = Math.abs((fillPrice - oraclePrice) / oraclePrice) * 100
       
+      // CRITICAL: Validate actual position size vs expected
+      // Phantom trade detection: Check if position is significantly smaller than expected
+      const actualSizeUSD = position.size * fillPrice
+      const expectedSizeUSD = params.sizeUSD
+      const sizeRatio = actualSizeUSD / expectedSizeUSD
+      
       console.log(`💰 Fill details:`)
       console.log(`   Fill price: $${fillPrice.toFixed(4)}`)
       console.log(`   Slippage: ${slippage.toFixed(3)}%`)
+      console.log(`   Expected size: $${expectedSizeUSD.toFixed(2)}`)
+      console.log(`   Actual size: $${actualSizeUSD.toFixed(2)}`)
+      console.log(`   Size ratio: ${(sizeRatio * 100).toFixed(1)}%`)
+      
+      // Flag as phantom if actual size is less than 50% of expected
+      const isPhantom = sizeRatio < 0.5
+      
+      if (isPhantom) {
+        console.error(`🚨 PHANTOM POSITION DETECTED!`)
+        console.error(`   Expected: $${expectedSizeUSD.toFixed(2)}`)
+        console.error(`   Actual: $${actualSizeUSD.toFixed(2)}`)
+        console.error(`   This indicates the order was rejected or partially filled by Drift`)
+      }
       
       return {
         success: true,
         transactionSignature: txSig,
         fillPrice,
-        fillSize: baseAssetSize,
+        fillSize: position.size, // Use actual size from Drift, not calculated
         slippage,
+        isPhantom,
+        actualSizeUSD,
       }
     } else {
       // Position not found yet (may be DRY_RUN mode)