fix(ui): fix centerTitle for ThreadHeader

packages/stream_chat_flutter/lib/src/thread_header.dart

@@ -115,6 +115,7 @@ class ThreadHeader extends StatelessWidget implements PreferredSizeWidget {
 
   @override
   Widget build(BuildContext context) {
+    final effectiveCenterTitle = _getEffectiveCenterTitle(Theme.of(context));
     final channelHeaderTheme = ChannelHeaderTheme.of(context);
 
     final defaultSubtitle = subtitle ??
@@ -161,6 +162,9 @@ class ThreadHeader extends StatelessWidget implements PreferredSizeWidget {
           width: 250,
           child: Column(
             mainAxisAlignment: MainAxisAlignment.center,
+            crossAxisAlignment: effectiveCenterTitle
+                ? CrossAxisAlignment.center
+                : CrossAxisAlignment.stretch,
             children: [
               title ??
                   Text(
@@ -187,4 +191,21 @@ class ThreadHeader extends StatelessWidget implements PreferredSizeWidget {
 
   @override
   final Size preferredSize;
+
+  bool _getEffectiveCenterTitle(ThemeData theme) {
+    if (centerTitle != null) return centerTitle!;
+    if (theme.appBarTheme.centerTitle != null) {
+      return theme.appBarTheme.centerTitle!;
+    }
+    switch (theme.platform) {
+      case TargetPlatform.android:
+      case TargetPlatform.fuchsia:
+      case TargetPlatform.linux:
+      case TargetPlatform.windows:
+        return false;
+      case TargetPlatform.iOS:
+      case TargetPlatform.macOS:
+        return actions == null || actions!.length < 2;
+    }
+  }
 }