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/firms/[id]/route.ts

@@ -31,6 +31,8 @@ export async function GET(
             minDayPnL: a.min_day_pnl,
             minTradingDays: a.min_trading_days,
             accountSize: a.account_size,
+            maxLoss: a.max_loss,
+            maxPositionSize: a.max_position_size,
         })),
     });
 }