style: doppelte Unterstriche in Closure-Parametern bereinigen

Dart 3 erlaubt mehrere Wildcard-Parameter mit demselben Namen "_" in
einem Scope, daher sind __ / ___ für ungenutzte Callback-Parameter
(pageBuilder, errorBuilder etc.) unnötig. Rein mechanische Änderung,
keine Verhaltensänderung.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/features/call/voice_channel.dart

@@ -689,7 +689,7 @@ class _ParticipantStrip extends StatelessWidget {
     return ListView.separated(
       scrollDirection: isVertical ? Axis.vertical : Axis.horizontal,
       itemCount: participants.length,
-      separatorBuilder: (_, __) => const SizedBox(width: 12, height: 12),
+      separatorBuilder: (_, _) => const SizedBox(width: 12, height: 12),
       itemBuilder: (context, i) => SizedBox(
         width: isVertical ? double.infinity : 101 * participants[i].aspectRatio,
         height: 101,

lib/features/chat/attachment_dialog.dart

@@ -30,9 +30,9 @@ class AttachmentDialog extends StatefulWidget {
           barrierLabel: 'Anhang',
           barrierColor: Colors.black54,
           transitionDuration: const Duration(milliseconds: 180),
-          pageBuilder: (_, __, ___) =>
+          pageBuilder: (_, _, _) =>
               AttachmentDialog(files: files, room: room, replyTo: replyTo),
-          transitionBuilder: (_, anim, __, child) {
+          transitionBuilder: (_, anim, _, child) {
             final curved =
                 CurvedAnimation(parent: anim, curve: Curves.easeOutBack);
             return FadeTransition(

lib/features/chat/document_viewer.dart

@@ -734,9 +734,9 @@ class _PdfFullscreenViewer extends StatefulWidget {
       opaque: true,
       barrierColor: Colors.black,
       transitionDuration: const Duration(milliseconds: 180),
-      pageBuilder: (_, __, ___) =>
+      pageBuilder: (_, _, _) =>
           _PdfFullscreenViewer(bytes: bytes, filename: filename, initialPage: initialPage),
-      transitionsBuilder: (_, anim, __, child) => FadeTransition(opacity: anim, child: child),
+      transitionsBuilder: (_, anim, _, child) => FadeTransition(opacity: anim, child: child),
     ));
   }
 

lib/features/chat/gif_sticker_picker.dart

@@ -538,7 +538,7 @@ class _GifStickerPickerState extends State<GifStickerPicker>
             child: Image.network(
               thumbUrl,
               fit: BoxFit.contain,
-              errorBuilder: (_, __, ___) => Container(color: _pt!.bg2),
+              errorBuilder: (_, _, _) => Container(color: _pt!.bg2),
             ),
           ),
         );
@@ -587,7 +587,7 @@ class _StickerCellState extends State<_StickerCell> {
               Image.network(
                 widget.piUrl,
                 fit: BoxFit.contain,
-                errorBuilder: (_, __, ___) => Container(color: pt.bg2),
+                errorBuilder: (_, _, _) => Container(color: pt.bg2),
               ),
               if (showOverlay)
                 Positioned(
@@ -666,7 +666,7 @@ class _GifCell extends StatelessWidget {
             fit: StackFit.expand,
             children: [
               Image.network(imageUrl, fit: BoxFit.cover,
-                errorBuilder: (_, __, ___) => Container(color: PyramidTheme.of(context).bg3)),
+                errorBuilder: (_, _, _) => Container(color: PyramidTheme.of(context).bg3)),
               if (isHovered || isFavorite)
                 Positioned(
                   top: 4, right: 4,