added a swipeable media gallery for chat and folder images and videos with server previews, on-demand originals and zoom, and marked document previews in chat so they no longer pass for photos

lib/routing/app_routes.dart

@@ -47,6 +47,8 @@ import '../widget/debug/cache_view.dart';
 import '../widget/debug/json_viewer.dart';
 import '../widget/file_viewer.dart';
 import '../widget/large_profile_picture_view.dart';
+import '../widget/media_gallery/gallery_source.dart';
+import '../widget/media_gallery/media_gallery_viewer.dart';
 import '../widget/user_avatar.dart';
 
 /// Single entry point for full-page navigations. Dialogs and bottom sheets
@@ -97,6 +99,19 @@ class AppRoutes {
     );
   }
 
+  /// Swipeable full-screen gallery; the viewer takes ownership of [source].
+  static void openMediaGallery(
+    BuildContext context, {
+    required GallerySource source,
+    required String initialKey,
+  }) {
+    pushScreen(
+      context,
+      withNavBar: false,
+      screen: MediaGalleryViewer(source: source, initialKey: initialKey),
+    );
+  }
+
   static void openCustomEvents(BuildContext context) {
     pushScreen(context, withNavBar: false, screen: const CustomEventsView());
   }