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>

backend/src/modules/investments/investments.service.ts

@@ -58,7 +58,7 @@ export class InvestmentsService {
       );
       if (primaryRows.length) {
         const primaryAccount = primaryRows[0];
-        const equityAccountNumber = fundType === 'reserve' ? 3100 : 3000;
+        const equityAccountNumber = fundType === 'reserve' ? '3100' : '3000';
         const equityRows = await this.tenant.query(
           'SELECT id FROM accounts WHERE account_number = $1',
           [equityAccountNumber],