Issue
Title: JSON export fails with PydanticSerializationUnexpectedValue for reclassified transactions
Description
When transactions are reclassified, the TransactionType field incorrectly stores a string representation of the enum rather than the enum object itself. This leads to a PydanticSerializationUnexpectedValue error when attempting to export data to JSON, particularly for merged descriptions. The expected behavior is for the TransactionType field to consistently hold the correct enum value, allowing JSON export to complete successfully without errors after reclassification.
Task
Modify the repository so that the issue described above is resolved. The task's test suite verifies your patch by applying it on top of the base commit 96ce8cdb5561 and running the modified tests.