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/database/tenant-schema.service.ts

@@ -35,7 +35,7 @@ export class TenantSchemaService {
       // Accounts (Chart of Accounts)
       `CREATE TABLE "${s}".accounts (
         id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
-        account_number INTEGER NOT NULL,
+        account_number VARCHAR(50) NOT NULL,
         name VARCHAR(255) NOT NULL,
         description TEXT,
         account_type VARCHAR(50) NOT NULL CHECK (account_type IN ('asset', 'liability', 'equity', 'income', 'expense')),