fix: Improve "Mark as Paid" UX with default split options

This commit fixes a significant usability issue where the "Mark as Paid" feature would behave incorrectly if the group had a default splitting option other than "Evenly".

Previously, when a user set a default splitting method for a group (e.g., "Unevenly" or "By Shares"), this default was also being applied to reimbursements. A reimbursement, by its nature, is a simple transfer between two parties and should always be split evenly. Applying a different split mode was not a valid operation and resulted in a confusing and disruptive user experience, making it difficult to mark debts as paid.

The fix is to update expense-form.tsx to ensure that when an expense is a reimbursement (isReimbursement: true), the splitMode is always hardcoded to 'EVENLY'. This change bypasses any group-level default splitting options for reimbursements, ensuring a smooth and intuitive workflow.

Fixes #365

Author: Uli-Z

src/app/groups/[groupId]/expenses/expense-form.tsx

@@ -230,7 +230,9 @@ export function ExpenseForm({
               : undefined,
           ],
           isReimbursement: true,
-          splitMode: defaultSplittingOptions.splitMode,
+          // Mark as paid reimbursements should always be split evenly
+          // independent of any stored default splitting options.
+          splitMode: 'EVENLY',
           saveDefaultSplittingOptions: false,
           documents: [],
           notes: '',