fix: persist notification preferences and clarify delivery controls

src/services/reminderPreferences.js

@@ -0,0 +1,13 @@
+export function validateReminderPreferences(value) {
+  if(!value || typeof value!=='object' || Array.isArray(value))throw new Error('Bildirim ayarları geçersiz.');
+  for(const key of ['pushEnabled','quietEnabled'])if(typeof value[key]!=='boolean')throw new Error('Bildirim seçimini kontrol edin.');
+  for(const key of ['quietStart','quietEnd'])if(typeof value[key]!=='string'||!/^([01]\d|2[0-3]):[0-5]\d$/.test(value[key]))throw new Error('Sessiz saatleri saat:dakika biçiminde girin.');
+  return value;
+}
+export function quietNow(preferences,now=new Date()) {
+  if(!preferences?.quietEnabled)return false;
+  try {validateReminderPreferences(preferences);}catch{return true;}
+  const minute=text=>Number(text.slice(0,2))*60+Number(text.slice(3));
+  const start=minute(preferences.quietStart),end=minute(preferences.quietEnd),current=now.getHours()*60+now.getMinutes();
+  return start<=end ? current>=start&&current<end : current>=start||current<end;
+}