Add max_position_size to account configs

- DB migration: ALTER TABLE account_configs ADD COLUMN max_position_size INTEGER NOT NULL DEFAULT 0
- Added max_position_size to AccountConfigRow, createAccountConfig, updateAccountConfig in lib/db.ts
- Added maxPositionSize to AccountConfig type in types.ts (0 = no limit)
- GET /api/firms/[id] now returns maxPositionSize per account
- POST /api/firms/[id]/accounts and PUT /api/account-configs/[id] accept maxPositionSize
- Firm settings page: new Max Contracts column (blank = no limit)
- auto-trade: contracts capped at maxPositionSize when > 0

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/api/account-configs/[id]/route.ts

@@ -20,9 +20,10 @@ export async function PUT(
         minTradingDays?: number;
         accountSize?: number;
         maxLoss?: number;
+        maxPositionSize?: number;
     };
 
-    const { prefix, profitTarget, consistency, minDayPnL, minTradingDays, accountSize, maxLoss } = body;
+    const { prefix, profitTarget, consistency, minDayPnL, minTradingDays, accountSize, maxLoss, maxPositionSize } = body;
 
     if (
         typeof prefix !== 'string' || !prefix.trim() ||
@@ -44,6 +45,7 @@ export async function PUT(
             minTradingDays,
             accountSize,
             maxLoss: maxLoss ?? 0,
+            maxPositionSize: maxPositionSize ?? 0,
         });
 
         if (!updated) {