feat(client): desktop 其他页精还原 + 整页 golden 闸

- stats_page 对照 dapp.jsx DStats 精对齐: padding 32/8、指标卡 padding 16/18·
  gap 14·值 mono 24、柱状图卡 padding 20/18·标题 13、柱 height 140(容 bar 86)·宽 34
- nodes_page 对照 DServers 微调: padding top 4、网格 gap 10(智能卡置顶保留, 符 §5)
- 新增 test/golden/desktop_pages_golden_test.dart: 用 macOS 平台覆盖 + 920×600 surface
  让 formFactor=desktop, 截 节点/统计/账户 三页整页 golden 作回归闸(连接页含旋转动画
  由组件级 golden 覆盖, 不在此截)

测试: flutter test 79 通过(+3 desktop 整页 golden), analyze 0 error

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/test/golden/desktop_pages_golden_test.dart

@@ -0,0 +1,62 @@
+// desktop_pages_golden_test.dart — desktop 整页 golden（节点/统计/账户）
+//
+// 用 debugDefaultTargetPlatformOverride=macOS + 920×600 surface 让 context.formFactor
+// 判定为 desktop，渲染 DesktopShell 各页，固化精还原成果作回归闸。
+// 连接页含连接键无限旋转动画，单独由组件级 golden 覆盖，此处不截。
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pangolin_vpn/bridge/vpn_bridge_mock.dart';
+import 'package:pangolin_vpn/bridge/vpn_bridge_provider.dart';
+import 'package:pangolin_vpn/pangolin_theme.dart';
+import 'package:pangolin_vpn/services/token_store.dart';
+import 'package:pangolin_vpn/shell/desktop_shell.dart';
+import 'package:pangolin_vpn/shell/home_shell.dart';
+import 'package:pangolin_vpn/state/auth_provider.dart';
+import 'package:pangolin_vpn/state/navigation_provider.dart';
+
+class _NullTokenStore implements TokenStore {
+  const _NullTokenStore();
+  @override
+  Future<void> saveTokens({required String access, required String refresh}) async {}
+  @override
+  Future<String?> loadAccessToken() async => null;
+  @override
+  Future<String?> loadRefreshToken() async => null;
+  @override
+  Future<void> clear() async {}
+}
+
+Future<void> _shoot(WidgetTester tester, NavView view, String name) async {
+  // 平台覆盖须在 test 体内设置并在结束前复位（否则触发 foundation 调试变量未复位断言）。
+  debugDefaultTargetPlatformOverride = TargetPlatform.macOS;
+  tester.view.physicalSize = const Size(920, 600);
+  tester.view.devicePixelRatio = 1.0;
+  addTearDown(tester.view.resetPhysicalSize);
+  addTearDown(tester.view.resetDevicePixelRatio);
+  try {
+    await tester.pumpWidget(ProviderScope(
+      overrides: [
+        tokenStoreProvider.overrideWithValue(const _NullTokenStore()),
+        vpnBridgeProvider.overrideWithValue(VpnBridgeMock()),
+        navViewProvider.overrideWith((ref) => view),
+      ],
+      child: MaterialApp(
+        debugShowCheckedModeBanner: false,
+        theme: PangolinTheme.light,
+        home: const HomeShell(),
+      ),
+    ));
+    await tester.pumpAndSettle();
+    await expectLater(find.byType(DesktopShell), matchesGoldenFile('goldens/$name.png'));
+  } finally {
+    debugDefaultTargetPlatformOverride = null;
+  }
+}
+
+void main() {
+  testWidgets('desktop 节点页', (t) => _shoot(t, NavView.servers, 'desktop_servers'));
+  testWidgets('desktop 统计页', (t) => _shoot(t, NavView.stats, 'desktop_stats'));
+  testWidgets('desktop 账户页', (t) => _shoot(t, NavView.account, 'desktop_account'));
+}