fix: use correct column name for accounts table in budget planning query

The accounts table uses 'name' not 'account_name'. Alias it correctly
in the getPlan JOIN query.

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

backend/src/modules/board-planning/budget-planning.service.ts

@@ -25,7 +25,7 @@ export class BudgetPlanningService {
 
     const plan = plans[0];
     const lines = await this.tenant.query(
-      `SELECT bpl.*, a.account_number, a.account_name, a.account_type, a.fund_type as account_fund_type
+      `SELECT bpl.*, a.account_number, a.name as account_name, a.account_type, a.fund_type as account_fund_type
        FROM budget_plan_lines bpl
        JOIN accounts a ON a.id = bpl.account_id
        WHERE bpl.budget_plan_id = $1