refactor(apps): 主题系统迁移至 ColorScheme + 扩展架构并支持 Dark Mode

apps/lib/shared/widgets/page_header.dart

@@ -42,10 +42,13 @@ class _BackButtonState extends State<BackButton> {
 
   @override
   Widget build(BuildContext context) {
-    final background = _isPressed ? AppColors.surfaceInfo : AppColors.white;
+    final colorScheme = Theme.of(context).colorScheme;
+    final background = _isPressed
+        ? colorScheme.secondaryContainer
+        : colorScheme.surface;
     final borderColor = _isPressed
-        ? AppColors.borderQuaternary
-        : AppColors.borderTertiary;
+        ? colorScheme.outlineVariant
+        : colorScheme.outline;
 
     return AnimatedScale(
       scale: _isPressed ? 0.96 : 1,
@@ -60,13 +63,13 @@ class _BackButtonState extends State<BackButton> {
           boxShadow: _isPressed
               ? const []
               : [
-                  const BoxShadow(
-                    color: AppColors.white,
+                  BoxShadow(
+                    color: colorScheme.surface,
                     blurRadius: AppRadius.sm,
-                    offset: Offset(0, -1),
+                    offset: const Offset(0, -1),
                   ),
                   BoxShadow(
-                    color: AppColors.slate200.withValues(alpha: 0.42),
+                    color: colorScheme.shadow.withValues(alpha: 0.42),
                     blurRadius: AppRadius.md,
                     offset: const Offset(0, AppSpacing.xs),
                   ),
@@ -76,39 +79,29 @@ class _BackButtonState extends State<BackButton> {
           width: AppSpacing.xl * 2,
           height: AppSpacing.xl * 2,
           child: Material(
-            color: Colors.transparent,
+            color: colorScheme.surface.withValues(alpha: 0),
             child: InkWell(
               borderRadius: BorderRadius.circular(AppRadius.full),
               onTap: widget.onPressed ?? () => Navigator.of(context).pop(),
               onTapDown: (_) {
-                if (_isPressed) {
-                  return;
-                }
-                setState(() {
-                  _isPressed = true;
-                });
+                if (_isPressed) return;
+                setState(() => _isPressed = true);
               },
               onTapCancel: () {
-                if (!_isPressed) {
-                  return;
-                }
-                setState(() {
-                  _isPressed = false;
-                });
+                if (!_isPressed) return;
+                setState(() => _isPressed = false);
               },
               onTapUp: (_) {
-                if (!_isPressed) {
-                  return;
-                }
-                setState(() {
-                  _isPressed = false;
-                });
+                if (!_isPressed) return;
+                setState(() => _isPressed = false);
               },
               child: Center(
                 child: Icon(
                   Icons.chevron_left,
                   size: AppSpacing.lg + AppSpacing.xs,
-                  color: _isPressed ? AppColors.blue600 : AppColors.slate700,
+                  color: _isPressed
+                      ? colorScheme.primary
+                      : colorScheme.onSurfaceVariant,
                 ),
               ),
             ),