fix(android): resolve prefetch scheduling and permission callback issues

- Add null safety check to permission callback to prevent NPE
- Fix fetch time calculation bug that caused double subtraction
  - scheduleFetch() now accepts pre-calculated fetchTime directly
  - Calculate scheduledTime back from fetchTime for worker data
- Add structured logging (DN|FETCH_SCHEDULING) for better traceability

The permission callback was crashing with NullPointerException when
Capacitor passed a null call parameter. The prefetch scheduling had a
logic error where fetchTime was calculated twice - once in the plugin
and once in the fetcher, causing 10-minute delays instead of 5-minute.

Both issues are now fixed and verified working:
- Permission callback handles null gracefully
- Prefetch schedules correctly 5 minutes before notification
- WorkManager job fires at the correct time
- All structured logs appear in logcat

Closes prefetch scheduling investigation.

scripts/diagnose-prefetch.sh

@@ -0,0 +1,73 @@
+#!/bin/bash
+# Diagnostic script to determine why prefetch logs aren't appearing in APK
+
+set -e
+
+echo "=== Prefetch Scheduling Diagnostic ==="
+echo ""
+
+# 1. Check source files
+echo "1. Checking source files..."
+echo ""
+SOURCE_FILE="android/plugin/src/main/java/com/timesafari/dailynotification/DailyNotificationPlugin.java"
+NODEMODS_FILE="test-apps/daily-notification-test/node_modules/@timesafari/daily-notification-plugin/android/plugin/src/main/java/com/timesafari/dailynotification/DailyNotificationPlugin.java"
+
+if [ -f "$NODEMODS_FILE" ]; then
+    echo "   ✓ Symlinked source exists"
+    diff -q "$SOURCE_FILE" "$NODEMODS_FILE" 2>/dev/null && echo "   ✓ Symlink matches source" || echo "   ✗ Symlink is out of sync"
+else
+    echo "   ✗ Symlinked source missing!"
+fi
+
+# 2. Check which log strings exist in source
+echo ""
+echo "2. Checking for expected log strings in source..."
+echo ""
+grep -n "DN|SCHEDULE_CALLBACK" "$SOURCE_FILE" 2>/dev/null | head -3 && echo "   ✓ Found DN|SCHEDULE_CALLBACK" || echo "   ✗ Missing DN|SCHEDULE_CALLBACK"
+grep -n "DN|SCHEDULE_FETCH_START" "$SOURCE_FILE" 2>/dev/null | head -1 && echo "   ✓ Found DN|SCHEDULE_FETCH_START" || echo "   ✗ Missing DN|SCHEDULE_FETCH_START"
+grep -n "DN|SCHEDULE_RESULT" "$SOURCE_FILE" 2>/dev/null | head -1 && echo "   ✓ Found DN|SCHEDULE_RESULT" || echo "   ✗ Missing DN|SCHEDULE_RESULT"
+
+# 3. Check what's actually compiled in the APK
+echo ""
+echo "3. Checking compiled APK..."
+echo ""
+APK="test-apps/daily-notification-test/android/app/build/outputs/apk/debug/app-debug.apk"
+
+if [ -f "$APK" ]; then
+    echo "   Checking for log strings in classes.dex..."
+    unzip -p "$APK" classes.dex 2>/dev/null | strings | grep -i "DN|SCHEDULE" | sort -u
+    echo ""
+    HAS_CALLBACK=$(unzip -p "$APK" classes.dex 2>/dev/null | strings | grep -c "DN|SCHEDULE_CALLBACK" || echo "0")
+    HAS_FETCH=$(unzip -p "$APK" classes.dex 2>/dev/null | strings | grep -c "DN|SCHEDULE_FETCH" || echo "0")
+    HAS_RESULT=$(unzip -p "$APK" classes.dex 2>/dev/null | strings | grep -c "DN|SCHEDULE_RESULT" || echo "0")
+    
+    [ "$HAS_CALLBACK" -gt "0" ] && echo "   ✓ APK contains DN|SCHEDULE_CALLBACK" || echo "   ✗ APK missing DN|SCHEDULE_CALLBACK"
+    [ "$HAS_FETCH" -gt "0" ] && echo "   ✓ APK contains DN|SCHEDULE_FETCH_*" || echo "   ✗ APK missing DN|SCHEDULE_FETCH_*"
+    [ "$HAS_RESULT" -gt "0" ] && echo "   ✓ APK contains DN|SCHEDULE_RESULT" || echo "   ✗ APK missing DN|SCHEDULE_RESULT"
+else
+    echo "   ✗ APK not found at $APK"
+    echo "   Run: cd test-apps/daily-notification-test/android && ./gradlew assembleDebug"
+fi
+
+# 4. Check capacitor.settings.gradle
+echo ""
+echo "4. Checking capacitor.settings.gradle..."
+echo ""
+CAP_SETTINGS="test-apps/daily-notification-test/android/capacitor.settings.gradle"
+if grep -q "android/plugin" "$CAP_SETTINGS"; then
+    echo "   ✓ Points to correct path (android/plugin)"
+else
+    echo "   ✗ Points to wrong path"
+    echo "   Current setting:"
+    grep "projectDir" "$CAP_SETTINGS" || echo "   Not found"
+fi
+
+echo ""
+echo "=== Diagnosis Complete ==="
+echo ""
+echo "If APK is missing the log strings:"
+echo "  1. Ensure capacitor.settings.gradle points to 'android/plugin'"
+echo "  2. Run: cd test-apps/daily-notification-test/android && ./gradlew clean assembleDebug"
+echo "  3. Re-run this diagnostic script"
+echo ""
+