Refactor code structure for improved readability and maintainability

frontend/src/views/DiaryView.vue

@@ -3245,7 +3245,7 @@ export default {
                 const now = new Date();
                 const currentTime = now.toLocaleTimeString('de-DE', { hour: '2-digit', minute: '2-digit', second: '2-digit' });
                 const currentHHMM = currentTime.slice(0, 5);
-                if (!this.trainingStart || !this.trainingEnd) {
+                if (!this.trainingStart) {
                     return;
                 }