fix: cancel existing alarm before scheduling new one for same scheduleId

- Cancel existing alarm for scheduleId before scheduling new one in scheduleDailyNotification
- Add verification logging to cancelNotification to confirm cancellation worked
- Ensures 'one per day' semantics when updating schedule time

Previously, when updating a schedule time:
- cleanupExistingNotificationSchedules() only canceled OTHER schedules (excluded current scheduleId)
- Old alarm for same scheduleId with different trigger time was not canceled
- Result: 2 alarms existed (old + new) violating 'one per day' semantics

The fix:
- In ScheduleHelper.scheduleDailyNotification(), cancel existing alarm for scheduleId BEFORE scheduling new one
- This ensures when updating schedule time, old alarm is canceled first
- Enhanced logging with DNP-CANCEL tag to track cancellation and verify it worked

Test 2 should now pass: updating schedule time will cancel old alarm before scheduling new one.

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

@@ -2635,6 +2635,12 @@ object ScheduleHelper {
         return try {
             val nextRunTime = calculateNextRunTime(config.schedule)
             
+            // CRITICAL: Cancel any existing alarm for this scheduleId BEFORE scheduling new one
+            // This ensures "one per day" semantics - when updating schedule time, old alarm is canceled
+            // The cleanupExistingNotificationSchedules() above only cancels OTHER schedules, not the current one
+            NotifyReceiver.cancelNotification(context, scheduleId)
+            Log.i("ScheduleHelper", "Cancelled existing alarm for scheduleId=$scheduleId before scheduling new one at $nextRunTime")
+            
             // Schedule AlarmManager notification as static reminder
             // (doesn't require cached content)
             NotifyReceiver.scheduleExactNotification(

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

@@ -481,7 +481,20 @@ class NotifyReceiver : BroadcastReceiver() {
                 PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE
             )
             alarmManager.cancel(pendingIntent)
-            Log.i(TAG, "Notification alarm cancelled: scheduleId=$scheduleId, triggerAt=$triggerAtMillis, requestCode=$requestCode")
+            Log.i(TAG, "DNP-CANCEL: Notification alarm cancelled: scheduleId=$scheduleId, triggerAt=$triggerAtMillis, requestCode=$requestCode")
+            
+            // Verify cancellation by checking if alarm still exists
+            val verifyIntent = PendingIntent.getBroadcast(
+                context,
+                requestCode,
+                intent,
+                PendingIntent.FLAG_NO_CREATE or PendingIntent.FLAG_IMMUTABLE
+            )
+            if (verifyIntent == null) {
+                Log.d(TAG, "DNP-CANCEL: ✅ Cancellation verified - no PendingIntent found for requestCode=$requestCode")
+            } else {
+                Log.w(TAG, "DNP-CANCEL: ⚠️ Cancellation may have failed - PendingIntent still exists for requestCode=$requestCode")
+            }
         }
         
         /**