fixed client-reported crashes in the pdf viewer, image picker and prosemirror images, mapped webdav errors to user messages and hardened keychain, cache and push stores against io failures

lib/notification/notification_service.dart

@@ -17,9 +17,11 @@ class NotificationService {
   Future<void> initializeNotifications() async {
     // Dedicated monochrome status-bar icon: launcher mipmaps are unusable as
     // small icons because Android renders only their alpha silhouette (a
-    // solid circle in the status bar).
+    // solid circle in the status bar). Bare resource name: the plugin resolves
+    // it via getIdentifier(name, "drawable", ...), and not every ROM strips a
+    // leading "@drawable/" there (reported as invalid_icon on some devices).
     const androidSettings = AndroidInitializationSettings(
-      '@drawable/ic_stat_notification',
+      'ic_stat_notification',
     );
 
     // iOS Talk category mirrors the Android inline reply + mark-as-read actions