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/view/pages/files/files.dart

@@ -140,8 +140,12 @@ class _FilesViewState extends State<_FilesView> {
                 return ListView.builder(
                   padding: EdgeInsets.zero,
                   itemCount: files.length,
-                  itemBuilder: (context, index) =>
-                      FileElement(files[index], widget.path, bloc.refresh),
+                  itemBuilder: (context, index) => FileElement(
+                    files[index],
+                    widget.path,
+                    bloc.refresh,
+                    siblings: files,
+                  ),
                 );
               },
             ),

lib/view/pages/files/widgets/file_element.dart

@@ -17,6 +17,8 @@ import '../../../../widget/confirm_dialog.dart';
 import '../../../../widget/demo_restricted.dart';
 import '../../../../widget/details_bottom_sheet.dart';
 import '../../../../widget/downloads/download_trigger.dart';
+import '../../../../widget/media_gallery/gallery_item.dart';
+import '../../../../widget/media_gallery/gallery_source.dart';
 import '../../../../widget/prompt_dialog.dart';
 import '../../talk/widgets/highlighted_linkify.dart';
 import '../data/webdav_path.dart';
@@ -33,11 +35,16 @@ class FileElement extends StatefulWidget {
   /// highlighted in the tile title. Used by the Files search delegate.
   final String? highlight;
 
+  /// The listing [file] belongs to, in display order; the media gallery pages
+  /// through its images and videos. Null opens the gallery on [file] alone.
+  final List<CacheableFile>? siblings;
+
   const FileElement(
     this.file,
     this.path,
     this.refetch, {
     this.highlight,
+    this.siblings,
     super.key,
   });
 
@@ -100,10 +107,7 @@ class _FileElementState extends State<FileElement>
 
   void _onTap() {
     if (widget.file.isDirectory) {
-      AppRoutes.openFolder(
-        context,
-        [...widget.path, widget.file.name],
-      );
+      AppRoutes.openFolder(context, [...widget.path, widget.file.name]);
       return;
     }
     if (guardDemoAction(context)) return;
@@ -111,12 +115,45 @@ class _FileElementState extends State<FileElement>
       confirmCancelDownload();
       return;
     }
+    if (galleryMediaKindOf(widget.file.name, mimeType: widget.file.mimeType) !=
+        null) {
+      _openGallery();
+      return;
+    }
     startDownload(
       name: widget.file.name,
       remoteFile: RemoteFileRef.fromCacheable(widget.file),
     );
   }
 
+  void _openGallery() {
+    final items = [
+      for (final file in widget.siblings ?? [widget.file])
+        if (!file.isDirectory) ?_galleryItem(file),
+    ];
+    AppRoutes.openMediaGallery(
+      context,
+      source: StaticGallerySource(items),
+      initialKey: widget.file.path,
+    );
+  }
+
+  static GalleryItem? _galleryItem(CacheableFile file) {
+    final kind = galleryMediaKindOf(file.name, mimeType: file.mimeType);
+    if (kind == null) return null;
+    final size = file.size;
+    final modified = file.modifiedAt;
+    return GalleryItem(
+      file: RemoteFileRef.fromCacheable(file),
+      kind: kind,
+      eTag: file.eTag,
+      subtitle: [
+        if (size != null) filesize(size),
+        if (modified != null) modified.formatDateTime(),
+      ].join(' · '),
+    );
+  }
+
   void _rename() {
     if (guardDemoAction(context)) return;
     showPromptDialog(