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/accounts/accounts.service.ts

@@ -92,7 +92,7 @@ export class AccountsService {
         const acctCredit = isDebitNormal ? 0 : absAmount;
 
         // Determine equity offset account based on fund type (auto-create if missing)
-        const equityAccountNumber = dto.fundType === 'reserve' ? 3100 : 3000;
+        const equityAccountNumber = dto.fundType === 'reserve' ? '3100' : '3000';
         const equityName = dto.fundType === 'reserve' ? 'Reserve Fund Balance' : 'Operating Fund Balance';
         let equityRows = await this.tenant.query(
           'SELECT id FROM accounts WHERE account_number = $1',
@@ -247,7 +247,7 @@ export class AccountsService {
     const fiscalPeriodId = periods[0].id;
 
     // Determine the equity offset account based on fund_type
-    const equityAccountNumber = account.fund_type === 'reserve' ? 3100 : 3000;
+    const equityAccountNumber = account.fund_type === 'reserve' ? '3100' : '3000';
     const equityRows = await this.tenant.query(
       'SELECT id, account_type FROM accounts WHERE account_number = $1',
       [equityAccountNumber],