fix: Add 99% safety buffer for 100% position sizing

Problem: Bot trying to use exact 100% of collateral causes InsufficientCollateral
errors due to Drift's margin calculation including fees, slippage buffers, etc.

Example:
- Collateral: $85.55
- Bot tries: $85.55 (100%)
- Margin required: $85.58 (includes fees)
- Result: Insufficient by $0.03 → Rejected

Drift UI works because it automatically applies safety buffer internally.

Solution: When user configures 100% position size, apply 99% safety buffer
to leave room for fees and slippage calculations.

Code change (config/trading.ts calculateActualPositionSize):
- Check if configuredSize >= 100
- Use 99% (0.99) instead of 100% (1.0)
- Log warning about safety buffer application

Impact: Bot can now use 'full' collateral without InsufficientCollateral errors.
Position size: $85.55 × 99% = $84.69 (well within margin requirements)

Math proof (from user's Drift UI):
- Available: $85.55
- UI max: $1,282.57 (15x leverage)
- Bot now: $84.69 × 15 = $1,270.35 (safe margin)

config/trading.ts

@@ -271,7 +271,16 @@ export function calculateActualPositionSize(
   }
   
   // Percentage of free collateral
-  const percentDecimal = configuredSize / 100
+  let percentDecimal = configuredSize / 100
+  
+  // CRITICAL: Safety buffer for 100% positions
+  // Drift's margin calculation includes fees and buffer, so 100% exact causes InsufficientCollateral
+  // Use 99% when user configures 100% to leave room for fees/slippage
+  if (configuredSize >= 100) {
+    percentDecimal = 0.99
+    console.log(`⚠️ Applying 99% safety buffer for 100% position (prevents InsufficientCollateral from fees/slippage)`)
+  }
+  
   const calculatedSize = freeCollateral * percentDecimal
   
   console.log(`📊 Percentage sizing: ${configuredSize}% of $${freeCollateral.toFixed(2)} = $${calculatedSize.toFixed(2)}`)