Allow users to undo/rollback a complete import batch

Easily rollback mistaken imports by deleting an entire batch at once.

Features:

• Use batchId to identify all transactions from a specific import

• DELETE endpoint: /api/v1/import/batch/{batchId}

• Confirmation dialog showing transaction count before deletion

• Automatic account balance recalculation after removal

Perfect for fixing import errors without manually finding and deleting individual transactions.