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/Sources/SourceDebugView.swift

@@ -81,8 +81,7 @@ struct SourceDebugView: View {
                     Label(model.isRunning ? "正在调试…" : "运行完整链路", systemImage: "play.fill")
                         .font(.headline).frame(maxWidth: .infinity)
                 }
-                .buttonStyle(.borderedProminent)
-                .tint(ReadingTheme.accent)
+                .readingProminentButtonStyle()
                 .disabled(model.isRunning || model.keyword.trimmingCharacters(in: .whitespacesAndNewlines).isEmpty)
             }
         }

App/Features/Sources/SourceEditorView.swift

@@ -44,11 +44,10 @@ struct SourceEditorView: View {
                         HStack {
                             ForEach(BookSourceEditorSchema.sections) { section in
                                 Button(section.title) { sectionID = section.id }
-                                    .buttonStyle(.bordered)
-                                    .tint(sectionID == section.id ? ReadingTheme.accent : .secondary)
+                                    .readingChoiceButtonStyle(isSelected: sectionID == section.id)
                             }
-                            Button("选项") { sectionID = "options" }.buttonStyle(.bordered)
-                                .tint(sectionID == "options" ? ReadingTheme.accent : .secondary)
+                            Button("选项") { sectionID = "options" }
+                                .readingChoiceButtonStyle(isSelected: sectionID == "options")
                         }.padding(.horizontal)
                     }.padding(.vertical, 6)
                     Form {

App/Features/Sources/SourceLoginView.swift

@@ -1,5 +1,6 @@
 @preconcurrency import WebKit
 import SwiftUI
+import UIKit
 
 struct SourceLoginView: View {
     let source: BookSource
@@ -74,6 +75,9 @@ private struct SourceLoginWebView: UIViewRepresentable {
         let configuration = WKWebViewConfiguration()
         configuration.websiteDataStore = .default()
         let webView = WKWebView(frame: .zero, configuration: configuration)
+        webView.isOpaque = false
+        webView.backgroundColor = UIColor(ReadingTheme.canvas)
+        webView.scrollView.backgroundColor = UIColor(ReadingTheme.canvas)
         webView.navigationDelegate = context.coordinator
         context.coordinator.installExistingCookies(in: webView) { webView.load(request) }
         return webView

App/Features/Sources/SourceManagementView.swift

@@ -61,7 +61,7 @@ struct SourceManagementView: View {
                     Text("新建书源，或从文件、链接、JSON、二维码导入。")
                 } actions: {
                     Button("导入书源", action: presentFileImporter)
-                        .buttonStyle(.borderedProminent)
+                        .readingProminentButtonStyle()
                 }
             } else {
                 List {