chore(db): Add migration to clean up inconsistent shares

This commit introduces a new data migration to address inconsistencies in existing expense data. It targets expenses where the  is set to 'EVENLY' but the associated  in the  table are not normalized to 1.

The migration ensures that all such expenses are corrected, guaranteeing data integrity and preventing calculation errors in features like CSV exports. This is a one-time cleanup that will be applied automatically when running .

Author: Uli-Z

prisma/migrations/20250701155133_cleanup_evenly_shares/migration.sql

@@ -0,0 +1,11 @@
+-- This migration cleans up existing data where the split mode is 'EVENLY'
+-- but the shares are not set to 1. This ensures data consistency for
+-- all expenses that should be split equally.
+
+UPDATE "ExpensePaidFor"
+SET "shares" = 1
+WHERE "expenseId" IN (
+  SELECT "id"
+  FROM "Expense"
+  WHERE "splitMode" = 'EVENLY'
+);