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/transactions/TransactionsPage.tsx

@@ -16,7 +16,7 @@ interface JournalEntryLine {
   id?: string;
   account_id: string;
   account_name?: string;
-  account_number?: number;
+  account_number?: string;
   debit: number;
   credit: number;
   memo: string;
@@ -38,7 +38,7 @@ interface JournalEntry {
 
 interface Account {
   id: string;
-  account_number: number;
+  account_number: string;
   name: string;
 }