Improve installment count selection in transaction form #64

Description

Improve the installment selection in the Add Transaction form.

The current installment field only provides a predefined set of options (from 1 to 12 and 24 installments). This limits users who need to register purchases with a different number of installments.

The installment quantity should be represented as a numeric input, allowing the user to enter/select the desired number of installments directly.

Expected Behavior

• Replace the current fixed installment options with a numeric input or another simple numeric selection mechanism.
• The user should be able to specify the number of installments freely, rather than being restricted to 1–12 and 24.
• The selected number must determine how many recurring installment transactions are generated for the purchase.
• The implementation details (input type, validation, UI component, maximum value, etc.) can be determined during development according to the existing architecture and UX patterns.

Acceptance Criteria

• The Add Transaction form allows the user to specify the installment count as a number.
• The user is no longer restricted to the current predefined 1–12 and 24 options.
• The selected installment count determines the number of transactions generated for the purchase.
• Existing installment functionality continues to work without regressions.
• Appropriate validation is implemented for invalid or unsupported values.
• The solution is consistent with the application's existing UI and design system.