fix(android): use TimeZone for default zone ID to support API 23

java.time.ZoneId is available only from API 26; on Android 6 it causes
NoClassDefFoundError when building NotificationContentEntity. Replaced
ZoneId.systemDefault().id with TimeZone.getDefault().id (Kotlin) and
getID() (Java) wherever we only need the system timezone ID string.

Same IANA ID and behavior on API 26+. No data or semantic change.
Worker/Scheduler still use java.time for date math; full API 23 there
would require ThreeTenABP or Calendar-based logic.

android/src/main/java/com/timesafari/dailynotification/DailyNotificationFetcher.java

@@ -229,7 +229,7 @@ public class DailyNotificationFetcher {
                     content.getTitle(),
                     content.getBody(),
                     content.getScheduledTime(),
-                    java.time.ZoneId.systemDefault().getId()
+                    java.util.TimeZone.getDefault().getID()
                 );
             entity.priority = mapPriority(content.getPriority());
             try {

android/src/main/java/com/timesafari/dailynotification/DailyNotificationPlugin.kt

@@ -2711,7 +2711,7 @@ object ScheduleHelper {
                     config.title ?: "Daily Notification",
                     config.body ?: "",
                     nextRunTime,
-                    java.time.ZoneId.systemDefault().id
+                    java.util.TimeZone.getDefault().id
                 )
                 entity.soundEnabled = config.sound ?: true
                 entity.vibrationEnabled = config.vibration ?: true

android/src/main/java/com/timesafari/dailynotification/DailyNotificationWorker.java

@@ -740,7 +740,7 @@ public class DailyNotificationWorker extends Worker {
                 content.getTitle(),
                 content.getBody(),
                 content.getScheduledTime(),
-                java.time.ZoneId.systemDefault().getId()
+                java.util.TimeZone.getDefault().getID()
             );
             entity.priority = mapPriorityToInt(content.getPriority());
             try {

android/src/main/java/com/timesafari/dailynotification/FetchWorker.kt

@@ -211,7 +211,7 @@ class FetchWorker(
                         title,
                         body,
                         notificationTime,
-                        java.time.ZoneId.systemDefault().id
+                        java.util.TimeZone.getDefault().id
                     )
                     entity.priority = 0 // default priority
                     entity.vibrationEnabled = true

android/src/main/java/com/timesafari/dailynotification/NotifyReceiver.kt

@@ -257,7 +257,7 @@ class NotifyReceiver : BroadcastReceiver() {
                         config.title,
                         config.body ?: (if (contentCache != null) String(contentCache.payload) else ""),
                         triggerAtMillis,
-                        java.time.ZoneId.systemDefault().id
+                        java.util.TimeZone.getDefault().id
                     )
                     entity.priority = when (config.priority) {
                         "high", "max" -> 2

android/src/main/java/com/timesafari/dailynotification/ReactivationManager.kt

@@ -273,7 +273,7 @@ class ReactivationManager(private val context: Context) {
                         "Daily Notification",
                         "Your daily update is ready",
                         scheduledTime,
-                        java.time.ZoneId.systemDefault().id
+                        java.util.TimeZone.getDefault().id
                     )
                     notification.deliveryStatus = "missed"
                     notification.lastDeliveryAttempt = System.currentTimeMillis()
@@ -1043,7 +1043,7 @@ class ReactivationManager(private val context: Context) {
                     "Daily Notification",
                     "Your daily update is ready",
                     scheduledTime,
-                    java.time.ZoneId.systemDefault().id
+                    java.util.TimeZone.getDefault().id
                 )
                 notification.deliveryStatus = "missed"
                 notification.lastDeliveryAttempt = System.currentTimeMillis()