fix(appearance): 完善深色模式和阅读页面对比度

- 区分按钮填充与图标颜色，统一书架、书源、搜索和阅读设置的选中态
- 调整编辑器语法高亮、键盘工具栏及统计卡片的浅深色显示
- 适配 RSS 正文和登录网页背景，保留书源自定义样式和页面状态
- 补充外观切换、页面对比度和管理页面的回归测试

App/Features/Books/BookDetailView.swift

@@ -194,7 +194,7 @@ struct BookDetailView: View {
                 .font(.body.weight(.medium))
                 .frame(maxWidth: .infinity, minHeight: 28)
         }
-        .buttonStyle(.borderedProminent)
+        .readingProminentButtonStyle()
         .disabled(model.chapters.isEmpty)
         Button {
             if library.contains(model.book) {
@@ -210,7 +210,7 @@ struct BookDetailView: View {
             .font(.subheadline)
             .frame(maxWidth: dynamicTypeSize.isAccessibilitySize ? .infinity : nil, minHeight: 28)
         }
-        .buttonStyle(.bordered)
+        .readingSecondaryButtonStyle()
     }
 
     @ViewBuilder