Add Application-level NetworkMonitor with extensive logging

- Create SimpleNotesApplication class for app-level lifecycle
- Move NetworkMonitor from Activity to Application context
- Add comprehensive logging to NetworkMonitor (all callbacks)
- Add logging to SyncWorker for debugging
- Remove NetworkMonitor from MainActivity (now in Application)
- Add Battery Optimization dialog in SettingsActivity
- Improve Notifications (showSyncInProgress, showSyncSuccess, showSyncError)

This should fix background sync issues - NetworkMonitor now runs
with Application context instead of Activity context, which should
survive when app is in background.

Debug with: adb logcat | grep -E 'NetworkMonitor|SyncWorker|SimpleNotesApp'

android/app/src/main/java/dev/dettmer/simplenotes/SimpleNotesApplication.kt

@@ -0,0 +1,41 @@
+package dev.dettmer.simplenotes
+
+import android.app.Application
+import android.util.Log
+import dev.dettmer.simplenotes.sync.NetworkMonitor
+import dev.dettmer.simplenotes.utils.NotificationHelper
+
+class SimpleNotesApplication : Application() {
+    
+    companion object {
+        private const val TAG = "SimpleNotesApp"
+    }
+    
+    private lateinit var networkMonitor: NetworkMonitor
+    
+    override fun onCreate() {
+        super.onCreate()
+        
+        Log.d(TAG, "🚀 Application onCreate()")
+        
+        // Initialize notification channel
+        NotificationHelper.createNotificationChannel(this)
+        Log.d(TAG, "✅ Notification channel created")
+        
+        // Initialize and start NetworkMonitor at application level
+        // CRITICAL: Use applicationContext, not 'this'!
+        networkMonitor = NetworkMonitor(applicationContext)
+        networkMonitor.startMonitoring()
+        
+        Log.d(TAG, "✅ NetworkMonitor initialized and started")
+    }
+    
+    override fun onTerminate() {
+        super.onTerminate()
+        
+        Log.d(TAG, "🛑 Application onTerminate()")
+        
+        // Clean up NetworkMonitor when app is terminated
+        networkMonitor.stopMonitoring()
+    }
+}