完成视频播放UI 调整

lib/shared/widgets/app_bar.dart

@@ -14,6 +14,8 @@ class AppPageBar extends StatelessWidget implements PreferredSizeWidget {
     this.backgroundImage,
     this.onBack,
     this.actions,
+    this.centerTitle = true,
+    this.titleSpacing,
   });
 
   final String title;
@@ -22,6 +24,10 @@ class AppPageBar extends StatelessWidget implements PreferredSizeWidget {
   final VoidCallback? onBack;
   final List<Widget>? actions;
 
+  /// 标题是否居中；false 时左对齐，紧随返回按钮。
+  final bool centerTitle;
+  final double? titleSpacing;
+
   @override
   Size get preferredSize => const Size.fromHeight(kToolbarHeight);
 
@@ -33,7 +39,8 @@ class AppPageBar extends StatelessWidget implements PreferredSizeWidget {
       backgroundColor: Colors.transparent,
       elevation: 0,
       scrolledUnderElevation: 0,
-      centerTitle: true,
+      centerTitle: centerTitle,
+      titleSpacing: titleSpacing,
       systemOverlayStyle: SystemUiOverlayStyle.light,
       flexibleSpace: SizedBox.expand(
         child: Image.asset(