feat: implement symbol-specific position sizing for multi-asset trading

- Extended MarketConfig with optional positionSize and leverage fields
- Configured ETH-PERP at  @ 1x leverage for minimal-risk data collection
- Created getPositionSizeForSymbol() helper function in config/trading.ts
- Integrated symbol-specific sizing into execute endpoint
- Added comprehensive guide in docs/guides/SYMBOL_SPECIFIC_SIZING.md

Purpose: Enable ETH trading for faster signal quality data collection
         while preserving SOL's profit-generation sizing (0 @ 10x)

Next: Create ETH alert in TradingView and restart bot

app/api/trading/execute/route.ts

@@ -166,6 +166,14 @@ export async function POST(request: NextRequest): Promise<NextResponse<ExecuteTr
     // Get trading configuration
     const config = getMergedConfig()
     
+    // Get symbol-specific position sizing
+    const { getPositionSizeForSymbol } = await import('@/config/trading')
+    const { size: positionSize, leverage } = getPositionSizeForSymbol(driftSymbol, config)
+    
+    console.log(`📐 Symbol-specific sizing for ${driftSymbol}:`)
+    console.log(`   Position size: $${positionSize}`)
+    console.log(`   Leverage: ${leverage}x`)
+    
     // Initialize Drift service if not already initialized
     const driftService = await initializeDriftService()
     
@@ -217,12 +225,12 @@ export async function POST(request: NextRequest): Promise<NextResponse<ExecuteTr
     }
 
     // Calculate position size with leverage
-    const positionSizeUSD = config.positionSize * config.leverage
+    const positionSizeUSD = positionSize * leverage
     
     console.log(`💰 Opening ${body.direction} position:`)
     console.log(`   Symbol: ${driftSymbol}`)
-    console.log(`   Base size: $${config.positionSize}`)
-    console.log(`   Leverage: ${config.leverage}x`)
+    console.log(`   Base size: $${positionSize}`)
+    console.log(`   Leverage: ${leverage}x`)
     console.log(`   Total position: $${positionSizeUSD}`)
 
     // Open position