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/MainActivity.kt

@@ -1,9 +1,12 @@
 package com.syncflow
 
+import android.Manifest
+import android.content.pm.PackageManager
 import android.os.Build
 import android.os.Bundle
 import androidx.activity.compose.setContent
 import androidx.activity.enableEdgeToEdge
+import androidx.activity.result.contract.ActivityResultContracts
 import androidx.appcompat.app.AppCompatActivity
 import androidx.biometric.BiometricManager
 import androidx.biometric.BiometricManager.Authenticators.BIOMETRIC_STRONG
@@ -49,10 +52,14 @@ class MainActivity : AppCompatActivity() {
     private var isLocked by mutableStateOf(false)
     private var showRetry by mutableStateOf(false)
 
+    private val requestNotificationPermission =
+        registerForActivityResult(ActivityResultContracts.RequestPermission()) { /* proceed regardless */ }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         installSplashScreen()
         super.onCreate(savedInstanceState)
         enableEdgeToEdge()
+        requestNotificationPermissionIfNeeded()
         setContent {
             SyncFlowTheme {
                 Surface(modifier = Modifier.fillMaxSize()) {
@@ -127,6 +134,16 @@ class MainActivity : AppCompatActivity() {
             BIOMETRIC_WEAK or DEVICE_CREDENTIAL
     }
 
+    private fun requestNotificationPermissionIfNeeded() {
+        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
+            if (ContextCompat.checkSelfPermission(this, Manifest.permission.POST_NOTIFICATIONS)
+                != PackageManager.PERMISSION_GRANTED
+            ) {
+                requestNotificationPermission.launch(Manifest.permission.POST_NOTIFICATIONS)
+            }
+        }
+    }
+
     private fun canAuthenticate(): Boolean {
         if (Build.VERSION.SDK_INT < Build.VERSION_CODES.R)
             return BiometricManager.from(this).canAuthenticate(BIOMETRIC_STRONG) == BiometricManager.BIOMETRIC_SUCCESS