Flexible budget import with auto-account creation and text-based account numbers

Change account_number from INTEGER to VARCHAR(50) to support segmented codes
like 30-3001-0000 used by real HOA accounting systems. Budget CSV import now:
- Auto-creates income/expense accounts from CSV when they don't exist
- Infers account_type and fund_type from account number prefix conventions
- Parses currency-formatted values ($48,065.21, $(13,000.00), $-, etc.)
- Reports created accounts back to the user

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

frontend/src/pages/reports/BudgetVsActualPage.tsx

@@ -8,7 +8,7 @@ import api from '../../services/api';
 
 interface BudgetVsActualLine {
   account_id: string;
-  account_number: number;
+  account_number: string;
   account_name: string;
   account_type: string;
   fund_type: string;