feat: fix notifications on Android 13+/16, add Log tab, fix ON_CHANGE detection

- Request POST_NOTIFICATIONS permission at runtime in MainActivity (primary fix
  for notifications never appearing on Android 13+ phones including Android 16)
- Register all 4 notification channels eagerly in SyncFlowApp.onCreate() instead
  of lazily inside workers
- Add FOREGROUND_SERVICE_SHORT_SERVICE permission + shortService foreground type
  for Android 16 foreground service compatibility
- Add global activity Log tab (new tab 2 in main nav) showing all sync events
  across all pairs, grouped by date with pair name, event icon, and file detail
- Fix FileWatchService ON_CHANGE detection: ContentObserver on SAF tree URIs only
  fires for SAF-API writes, not raw filesystem writes. Now resolves primary:/*
  tree URIs to /storage/emulated/0/* and uses FileObserver for reliable detection
- Bump version to 1.0.21 (build 22)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/src/main/kotlin/com/syncflow/SyncFlowApp.kt

@@ -1,6 +1,9 @@
 package com.syncflow
 
 import android.app.Application
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.content.Context
 import androidx.hilt.work.HiltWorkerFactory
 import androidx.work.Configuration
 import com.syncflow.data.db.SyncPairDao
@@ -22,6 +25,7 @@ class SyncFlowApp : Application(), Configuration.Provider {
     override fun onCreate() {
         super.onCreate()
         if (BuildConfig.DEBUG) Timber.plant(Timber.DebugTree())
+        createNotificationChannels()
         // Start file watcher on every app launch for any existing ON_CHANGE pairs
         CoroutineScope(Dispatchers.IO).launch {
             val hasOnChange = syncPairDao.getEnabled().any { it.scheduleType == ScheduleType.ON_CHANGE }
@@ -29,6 +33,27 @@ class SyncFlowApp : Application(), Configuration.Provider {
         }
     }
 
+    private fun createNotificationChannels() {
+        val nm = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
+        listOf(
+            NotificationChannel("sync_progress", "Sync progress", NotificationManager.IMPORTANCE_LOW).apply {
+                description = "Shown while a sync is running"
+            },
+            NotificationChannel("sync_complete", "Sync complete", NotificationManager.IMPORTANCE_LOW).apply {
+                description = "Summary after each successful sync"
+            },
+            NotificationChannel("sync_alerts", "Sync errors", NotificationManager.IMPORTANCE_DEFAULT).apply {
+                description = "Alerts for sync failures and conflicts"
+            },
+            NotificationChannel("sync_watching", "File watching", NotificationManager.IMPORTANCE_MIN).apply {
+                description = "Background service watching folders for changes"
+                setShowBadge(false)
+            },
+        ).forEach { channel ->
+            if (nm.getNotificationChannel(channel.id) == null) nm.createNotificationChannel(channel)
+        }
+    }
+
     override val workManagerConfiguration: Configuration
         get() = Configuration.Builder()
             .setWorkerFactory(workerFactory)