Remove spent Field from Budget Model

The spent field in the Budget model is no longer needed as we focus on tracking budgets based on budget_limit alone. The spent field adds unnecessary complexity to our data structure and is not utilised in our current budgeting functionality.

Tasks:

• Remove the spent field from the Budget model.
• Ensure the removal does not affect existing functionality.

Acceptance Criteria:

• The Budget model no longer includes the spent field.
• All related functionality operates correctly after the change.
• Database schema reflects the removal of the field.