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/talk/widgets/chat_file_attachment.dart

@@ -0,0 +1,149 @@
+import 'package:cached_network_image/cached_network_image.dart';
+import 'package:flutter/material.dart';
+
+import '../../../../api/marianumcloud/talk/chat/get_chat_response.dart';
+import '../../../../model/endpoint_data.dart';
+import '../../../../session/session_manager.dart';
+import '../../../../widget/media_gallery/gallery_item.dart';
+import '../../files/data/file_type_icon.dart';
+
+/// File attachment in a chat bubble. Only what the media gallery pages through
+/// renders as a plain picture; other previews (documents, audio covers) carry
+/// a name strip so they don't pass for photos.
+class ChatFileAttachment extends StatelessWidget {
+  final RichObjectString file;
+
+  const ChatFileAttachment({required this.file, super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final kind = galleryMediaKindOf(file.name, mimeType: file.mimetype);
+    return CachedNetworkImage(
+      imageUrl:
+          '${EndpointData().nextcloud().origin()}/index.php/core/preview?fileId=${file.id}&x=130&y=-1&a=1',
+      httpHeaders: SessionManager().requireNextcloud().authHeaders,
+      alignment: Alignment.center,
+      fadeInDuration: Duration.zero,
+      fadeOutDuration: Duration.zero,
+      errorListener: (_) {},
+      placeholder: (context, url) => const Padding(
+        padding: EdgeInsets.all(15),
+        child: SizedBox(width: 50, child: LinearProgressIndicator()),
+      ),
+      imageBuilder: switch (kind) {
+        GalleryMediaKind.image => null,
+        GalleryMediaKind.video => (context, image) => Stack(
+          alignment: Alignment.center,
+          children: [
+            Image(image: image),
+            const _PlayBadge(),
+          ],
+        ),
+        null => (context, image) => Stack(
+          children: [
+            Image(image: image),
+            Positioned(
+              left: 0,
+              right: 0,
+              bottom: 0,
+              child: _NameStrip(name: file.name),
+            ),
+          ],
+        ),
+      },
+      errorWidget: (context, url, error) => kind == GalleryMediaKind.video
+          ? const _VideoPlaceholder()
+          : _FileRow(name: file.name),
+    );
+  }
+}
+
+class _PlayBadge extends StatelessWidget {
+  const _PlayBadge();
+
+  @override
+  Widget build(BuildContext context) => const DecoratedBox(
+    decoration: BoxDecoration(color: Colors.black54, shape: BoxShape.circle),
+    child: Padding(
+      padding: EdgeInsets.all(6),
+      child: Icon(Icons.play_arrow, color: Colors.white, size: 28),
+    ),
+  );
+}
+
+/// Same footprint as a typical preview, so videos without a server thumbnail
+/// still read as media.
+class _VideoPlaceholder extends StatelessWidget {
+  const _VideoPlaceholder();
+
+  @override
+  Widget build(BuildContext context) => Container(
+    width: 130,
+    height: 90,
+    decoration: BoxDecoration(
+      color: Colors.black87,
+      borderRadius: BorderRadius.circular(4),
+    ),
+    alignment: Alignment.center,
+    child: const Stack(
+      alignment: Alignment.center,
+      children: [
+        Icon(Icons.movie_outlined, color: Colors.white38, size: 56),
+        _PlayBadge(),
+      ],
+    ),
+  );
+}
+
+class _NameStrip extends StatelessWidget {
+  final String name;
+
+  const _NameStrip({required this.name});
+
+  @override
+  Widget build(BuildContext context) => ColoredBox(
+    color: Colors.black54,
+    child: Padding(
+      padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 3),
+      child: Row(
+        children: [
+          Icon(iconForFileName(name), size: 14, color: Colors.white),
+          const SizedBox(width: 4),
+          Expanded(
+            child: Text(
+              name,
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              style: const TextStyle(color: Colors.white, fontSize: 11),
+            ),
+          ),
+        ],
+      ),
+    ),
+  );
+}
+
+class _FileRow extends StatelessWidget {
+  final String name;
+
+  const _FileRow({required this.name});
+
+  @override
+  Widget build(BuildContext context) => Row(
+    mainAxisSize: MainAxisSize.min,
+    crossAxisAlignment: CrossAxisAlignment.center,
+    children: [
+      const Icon(Icons.file_open_outlined, size: 35),
+      const SizedBox(width: 10),
+      Flexible(
+        child: Text(
+          name,
+          maxLines: 2,
+          overflow: TextOverflow.ellipsis,
+          style: const TextStyle(fontWeight: FontWeight.bold),
+        ),
+      ),
+      const SizedBox(width: 10),
+    ],
+  );
+}