feat(app): 完善播放协议搜索与空状态

lib/core/widgets/empty_state.dart

@@ -115,7 +115,6 @@ class _EmptyCopy extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final scheme = Theme.of(context).colorScheme;
     return Column(
       mainAxisSize: MainAxisSize.min,
       children: [
@@ -126,10 +125,10 @@ class _EmptyCopy extends StatelessWidget {
             maxLines: 2,
             overflow: TextOverflow.ellipsis,
             textAlign: TextAlign.center,
-            style: TextStyle(
-              color: scheme.onSurface,
+            style: const TextStyle(
+              color: AppColors.textTertiary,
               fontSize: 15,
-              fontWeight: FontWeight.w600,
+              fontWeight: FontWeight.w400,
               height: 1.35,
             ),
           ),

lib/core/widgets/subpage_header.dart

@@ -13,7 +13,9 @@ const double _titleFontSize = 18;
 const double _subtitleFontSize = 12;
 const double _actionGap = 8;
 const double _iconSize = 22;
+const double _backIconSize = 34;
 const double _iconWeight = 600;
+const double _backIconWeight = 400;
 const double _shadowBlur = 8;
 
 /// 二级页面统一圆形操作按钮，返回、分享和更多共用同一尺寸与表面样式。
@@ -24,6 +26,8 @@ class AppSubpageCircleButton extends StatelessWidget {
     required this.tooltip,
     required this.icon,
     required this.onPressed,
+    this.iconSize = _iconSize,
+    this.iconWeight = _iconWeight,
     this.dark = false,
   });
 
@@ -31,6 +35,8 @@ class AppSubpageCircleButton extends StatelessWidget {
   final String tooltip;
   final IconData icon;
   final VoidCallback onPressed;
+  final double iconSize;
+  final double iconWeight;
   final bool dark;
 
   @override
@@ -65,8 +71,8 @@ class AppSubpageCircleButton extends StatelessWidget {
                 child: Icon(
                   icon,
                   color: dark ? AppColors.onSurface : AppColors.textPrimary,
-                  size: _iconSize,
-                  weight: _iconWeight,
+                  size: iconSize,
+                  weight: iconWeight,
                 ),
               ),
             ),
@@ -96,6 +102,8 @@ class AppSubpageBackButton extends StatelessWidget {
       buttonKey: backKey,
       tooltip: MaterialLocalizations.of(context).backButtonTooltip,
       icon: Icons.chevron_left_rounded,
+      iconSize: _backIconSize,
+      iconWeight: _backIconWeight,
       dark: dark,
       onPressed: onBack ?? () => Navigator.of(context).maybePop(),
     );