Wrap transaction_type in col() for notin_ filter

SQLModel enum columns need col() to expose SQLAlchemy operators like
notin_. Without it the agent tool raised at query build time and the
chat card flashed away.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/agent/tools.py

@@ -119,7 +119,7 @@ def get_recent_transactions(
     """Recent transactions, newest first. Use filters to narrow down. For
     billing-cycle scoped totals prefer get_cycle_summary."""
     q = select(Transaction).where(
-        Transaction.transaction_type.notin_(
+        col(Transaction.transaction_type).notin_(
             [TransactionType.SALARY, TransactionType.DEPOSITO]
         )
     )