feat: Implement percentage-based position sizing

- Add usePercentageSize flag to SymbolSettings and TradingConfig
- Add calculateActualPositionSize() and getActualPositionSizeForSymbol() helpers
- Update execute and test endpoints to calculate position size from free collateral
- Add SOLANA_USE_PERCENTAGE_SIZE, ETHEREUM_USE_PERCENTAGE_SIZE, USE_PERCENTAGE_SIZE env vars
- Configure SOL to use 100% of portfolio (auto-adjusts to available balance)
- Fix TypeScript errors: replace fillNotionalUSD with actualSizeUSD
- Remove signalQualityVersion and fullyClosed references (not in interfaces)
- Add comprehensive documentation in PERCENTAGE_SIZING_FEATURE.md

Benefits:
- Prevents insufficient collateral errors by using available balance
- Auto-scales positions as account grows/shrinks
- Maintains risk proportional to capital
- Flexible per-symbol configuration (SOL percentage, ETH fixed)

config/trading.ts

@@ -8,12 +8,14 @@ export interface SymbolSettings {
   enabled: boolean
   positionSize: number
   leverage: number
+  usePercentageSize?: boolean // If true, positionSize is % of portfolio (0-100)
 }
 
 export interface TradingConfig {
   // Position sizing (global fallback)
-  positionSize: number // USD amount to trade
+  positionSize: number // USD amount to trade (or percentage if usePercentageSize=true)
   leverage: number // Leverage multiplier
+  usePercentageSize: boolean // If true, positionSize is % of free collateral
   
   // Per-symbol settings
   solana?: SymbolSettings
@@ -93,19 +95,22 @@ export interface MarketConfig {
 // Default configuration for 5-minute scalping with $1000 capital and 10x leverage
 export const DEFAULT_TRADING_CONFIG: TradingConfig = {
   // Position sizing (global fallback)
-  positionSize: 50, // $50 base capital (SAFE FOR TESTING)
+  positionSize: 50, // $50 base capital (SAFE FOR TESTING) OR percentage if usePercentageSize=true
   leverage: 10, // 10x leverage = $500 position size
+  usePercentageSize: false, // False = fixed USD, True = percentage of portfolio
   
   // Per-symbol settings
   solana: {
     enabled: true,
-    positionSize: 210, // $210 base capital
+    positionSize: 210, // $210 base capital OR percentage if usePercentageSize=true
     leverage: 10, // 10x leverage = $2100 notional
+    usePercentageSize: false,
   },
   ethereum: {
     enabled: true,
     positionSize: 4, // $4 base capital (DATA ONLY - minimum size)
     leverage: 1, // 1x leverage = $4 notional
+    usePercentageSize: false,
   },
   
   // Risk parameters (wider for DEX slippage/wicks)
@@ -248,6 +253,85 @@ export function getPositionSizeForSymbol(symbol: string, baseConfig: TradingConf
   }
 }
 
+/**
+ * Calculate actual USD position size from percentage or fixed amount
+ * @param configuredSize - The configured size (USD or percentage)
+ * @param usePercentage - Whether configuredSize is a percentage
+ * @param freeCollateral - Available collateral in USD (from Drift account)
+ * @returns Actual USD size to use for the trade
+ */
+export function calculateActualPositionSize(
+  configuredSize: number,
+  usePercentage: boolean,
+  freeCollateral: number
+): number {
+  if (!usePercentage) {
+    // Fixed USD amount
+    return configuredSize
+  }
+  
+  // Percentage of free collateral
+  const percentDecimal = configuredSize / 100
+  const calculatedSize = freeCollateral * percentDecimal
+  
+  console.log(`📊 Percentage sizing: ${configuredSize}% of $${freeCollateral.toFixed(2)} = $${calculatedSize.toFixed(2)}`)
+  
+  return calculatedSize
+}
+
+/**
+ * Get actual position size for symbol with percentage support
+ * This is the main function to use when opening positions
+ */
+export async function getActualPositionSizeForSymbol(
+  symbol: string,
+  baseConfig: TradingConfig,
+  freeCollateral: number
+): Promise<{ size: number; leverage: number; enabled: boolean; usePercentage: boolean }> {
+  let symbolSettings: { size: number; leverage: number; enabled: boolean }
+  let usePercentage = false
+  
+  // Get symbol-specific settings
+  if (symbol === 'SOL-PERP' && baseConfig.solana) {
+    symbolSettings = {
+      size: baseConfig.solana.positionSize,
+      leverage: baseConfig.solana.leverage,
+      enabled: baseConfig.solana.enabled,
+    }
+    usePercentage = baseConfig.solana.usePercentageSize ?? false
+  } else if (symbol === 'ETH-PERP' && baseConfig.ethereum) {
+    symbolSettings = {
+      size: baseConfig.ethereum.positionSize,
+      leverage: baseConfig.ethereum.leverage,
+      enabled: baseConfig.ethereum.enabled,
+    }
+    usePercentage = baseConfig.ethereum.usePercentageSize ?? false
+  } else {
+    // Fallback to market-specific or global config
+    const marketConfig = getMarketConfig(symbol)
+    symbolSettings = {
+      size: marketConfig.positionSize ?? baseConfig.positionSize,
+      leverage: marketConfig.leverage ?? baseConfig.leverage,
+      enabled: true,
+    }
+    usePercentage = baseConfig.usePercentageSize
+  }
+  
+  // Calculate actual size
+  const actualSize = calculateActualPositionSize(
+    symbolSettings.size,
+    usePercentage,
+    freeCollateral
+  )
+  
+  return {
+    size: actualSize,
+    leverage: symbolSettings.leverage,
+    enabled: symbolSettings.enabled,
+    usePercentage,
+  }
+}
+
 /**
  * Calculate dynamic TP2 level based on ATR (Average True Range)
  * Higher ATR = higher volatility = larger TP2 target to capture big moves
@@ -324,6 +408,10 @@ export function getConfigFromEnv(): Partial<TradingConfig> {
       ? parseFloat(process.env.MAX_POSITION_SIZE_USD) 
       : undefined,
     
+    usePercentageSize: process.env.USE_PERCENTAGE_SIZE
+      ? process.env.USE_PERCENTAGE_SIZE === 'true'
+      : undefined,
+    
     // Per-symbol settings from ENV
     solana: {
       enabled: process.env.SOLANA_ENABLED !== 'false',
@@ -333,6 +421,9 @@ export function getConfigFromEnv(): Partial<TradingConfig> {
       leverage: process.env.SOLANA_LEVERAGE
         ? parseInt(process.env.SOLANA_LEVERAGE)
         : 10,
+      usePercentageSize: process.env.SOLANA_USE_PERCENTAGE_SIZE
+        ? process.env.SOLANA_USE_PERCENTAGE_SIZE === 'true'
+        : false,
     },
     ethereum: {
       enabled: process.env.ETHEREUM_ENABLED !== 'false',
@@ -342,6 +433,9 @@ export function getConfigFromEnv(): Partial<TradingConfig> {
       leverage: process.env.ETHEREUM_LEVERAGE
         ? parseInt(process.env.ETHEREUM_LEVERAGE)
         : 1,
+      usePercentageSize: process.env.ETHEREUM_USE_PERCENTAGE_SIZE
+        ? process.env.ETHEREUM_USE_PERCENTAGE_SIZE === 'true'
+        : false,
     },
     leverage: process.env.LEVERAGE 
       ? parseInt(process.env.LEVERAGE)