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/data/db/SyncEventDao.kt

@@ -9,6 +9,9 @@ interface SyncEventDao {
     @Query("SELECT * FROM sync_events WHERE syncPairId = :pairId ORDER BY timestamp DESC LIMIT :limit")
     fun observeRecent(pairId: Long, limit: Int = 200): Flow<List<SyncEventEntity>>
 
+    @Query("SELECT * FROM sync_events ORDER BY timestamp DESC LIMIT :limit")
+    fun observeAll(limit: Int = 500): Flow<List<SyncEventEntity>>
+
     @Insert
     suspend fun insert(entity: SyncEventEntity): Long