Sets default currency to EUR

Ensures that the currency field defaults to EUR in both the expense and receivable dialogs.

This provides a better user experience by pre-selecting a common currency, preventing the user from having to manually choose it every time.

static/js/index.js

@@ -27,7 +27,7 @@ window.app = Vue.createApp({
         expenseAccount: '',
         isEquity: false,
         reference: '',
-        currency: null,
+        currency: 'EUR',
         loading: false
       },
       payDialog: {
@@ -973,7 +973,7 @@ window.app = Vue.createApp({
       this.expenseDialog.expenseAccount = ''
       this.expenseDialog.isEquity = false
       this.expenseDialog.reference = ''
-      this.expenseDialog.currency = null
+      this.expenseDialog.currency = 'EUR'
     },
     resetReceivableDialog() {
       this.receivableDialog.selectedUser = ''