feat(schedule): improve predefined schedule groups

static/src/app/base/storage.ts

@@ -17,15 +17,16 @@ export class DataStorage<T extends { id: string }> {
     return this.readValues();
   }
 
-  add(value: T) {
+  add(value: T): boolean {
     const values = this.readValues();
     for (const v of values) {
       if (v.id == value.id) {
-        return;
+        return false;
       }
     }
     values.push(value);
     this.writeValues(values);
+    return true;
   }
 
   remove(id: string) {