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/ui/log/LogViewModel.kt

@@ -0,0 +1,29 @@
+package com.syncflow.ui.log
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import com.syncflow.data.db.SyncEventDao
+import com.syncflow.data.db.SyncPairDao
+import com.syncflow.data.db.entities.SyncEventEntity
+import dagger.hilt.android.lifecycle.HiltViewModel
+import kotlinx.coroutines.flow.SharingStarted
+import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.stateIn
+import javax.inject.Inject
+
+data class LogEntry(val event: SyncEventEntity, val pairName: String)
+
+@HiltViewModel
+class LogViewModel @Inject constructor(
+    syncEventDao: SyncEventDao,
+    syncPairDao: SyncPairDao,
+) : ViewModel() {
+
+    val entries = combine(
+        syncEventDao.observeAll(500),
+        syncPairDao.observeAll(),
+    ) { events, pairs ->
+        val pairNames = pairs.associateBy({ it.id }, { it.name })
+        events.map { LogEntry(it, pairNames[it.syncPairId] ?: "Unknown") }
+    }.stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), emptyList())
+}