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/AndroidManifest.xml

@@ -8,6 +8,7 @@
     <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" tools:ignore="ScopedStorage" />
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE_DATA_SYNC" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_SHORT_SERVICE" />
     <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
     <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
     <uses-permission android:name="android.permission.WAKE_LOCK" />
@@ -71,13 +72,13 @@
         <!-- File watcher for ON_CHANGE sync pairs -->
         <service
             android:name=".worker.FileWatchService"
-            android:foregroundServiceType="dataSync"
+            android:foregroundServiceType="dataSync|shortService"
             android:exported="false" />
 
         <!-- Required on API 29+ so WorkManager can start a typed foreground service -->
         <service
             android:name="androidx.work.impl.foreground.SystemForegroundService"
-            android:foregroundServiceType="dataSync"
+            android:foregroundServiceType="dataSync|shortService"
             tools:node="merge" />
 
         <!-- Remove WorkManager's default initializer — app uses on-demand init via Configuration.Provider -->