feat(client): 三端布局架构 + macOS 桌面端 + app 图标

三端布局(mobile/tablet/desktop):
- core/responsive/form_factor.dart 形态判定 + shell/ 分发器(home_shell→desktop/mobile)
- desktop_shell 对照 ui_kits/desktop/dapp.jsx: 侧栏204·6项 + 套餐卡 + 顶栏(标题/状态/主题切换) + 连接页居中单列
- 新增组件 nav_sidebar / plan_badge_card / content_top_bar / bottom_tab_bar
- 新增一级页 contact_page / settings_page; navigation_provider(NavView)
- 删除旧 widgets/home_shell.dart(逻辑迁入 shell/)

macOS 桌面端:
- 窗口默认 920×600 + 最小 720×560(MainFlutterWindow.swift)
- app 图标替换为穿山甲(AppIcon.appiconset 全套, 由 app-icon.svg 渲染)

其余(本会话):
- Phase2 接线: auth_api/token_store/auth_provider/vpn_bridge_provider + 真实 connection/nodes
- lucide_icons 兼容补丁(packages/lucide_icons_patched) 修复 IconData final 报错
- 测试修复: connect_passthrough(UTF-8) / harness / golden @Skip
- l10n 新增 settingsTitle

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

client/lib/state/nodes_provider.dart

@@ -1,12 +1,71 @@
-// nodes_provider.dart — 节点清单 + 当前选择(含智能选择 AUTO)
+// nodes_provider.dart — 节点清单 + 当前选择
+//
+// 从 GET /v1/nodes 拉取节点列表；认证后自动刷新。
+// 未登录 / 加载中时退回演示节点（kDemoNodes）保证 UI 正常显示。
+import 'dart:convert';
+
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:http/http.dart' as http;
 
 import '../models/node.dart';
+import 'auth_provider.dart';
 
-/// 可用节点(演示数据;接口就绪后替换为 nodes API)。
-final nodesProvider = Provider<List<Node>>((ref) => kDemoNodes);
+// ── API base URL（由 --dart-define 注入）──────────────────────────
+
+const _kApiUrl = String.fromEnvironment(
+  'PANGOLIN_API_URL',
+  defaultValue: 'http://localhost:8080',
+);
+
+// ── 节点列表 AsyncNotifier ────────────────────────────────────────
+
+class NodesNotifier extends AsyncNotifier<List<Node>> {
+  @override
+  Future<List<Node>> build() async {
+    final auth = ref.watch(authProvider);
+    if (!auth.isLoggedIn) return kDemoNodes;
+    return _fetchNodes(auth.accessToken!);
+  }
+
+  Future<void> refresh() async {
+    state = const AsyncLoading();
+    final auth = ref.read(authProvider);
+    if (!auth.isLoggedIn) {
+      state = AsyncData(kDemoNodes);
+      return;
+    }
+    state = await AsyncValue.guard(() => _fetchNodes(auth.accessToken!));
+  }
+
+  static Future<List<Node>> _fetchNodes(String accessToken) async {
+    final uri = Uri.parse('$_kApiUrl/v1/nodes');
+    final resp = await http.get(uri, headers: {
+      'Authorization': 'Bearer $accessToken',
+    }).timeout(const Duration(seconds: 10));
+
+    if (resp.statusCode != 200) return kDemoNodes;
+
+    final body = jsonDecode(resp.body) as Map<String, dynamic>;
+    final rawList = body['nodes'] as List<dynamic>? ?? [];
+    return rawList.map((e) {
+      final m = e as Map<String, dynamic>;
+      return Node(
+        uuid: m['id'] as String? ?? '',
+        code: m['region'] as String? ?? '??',
+        nameZh: m['name_zh'] as String? ?? '',
+        nameEn: m['name_en'] as String? ?? '',
+        tier: m['tier'] as String? ?? 'free',
+        ping: 0, // 延迟由探针数据填充；MVP 默认 0
+      );
+    }).toList();
+  }
+}
+
+final nodesProvider =
+    AsyncNotifierProvider<NodesNotifier, List<Node>>(NodesNotifier.new);
+
+// ── 当前选中的节点 UUID；'AUTO' 表示智能选择（默认）─────────────────
 
-/// 当前选中的节点 code;`AUTO` 表示智能选择(默认)。
 final selectedNodeCodeProvider = StateProvider<String>((ref) => kSmartNodeCode);
 
 /// 是否处于智能选择。
@@ -14,11 +73,15 @@ final isSmartSelectProvider = Provider<bool>(
   (ref) => ref.watch(selectedNodeCodeProvider) == kSmartNodeCode,
 );
 
-/// 实际生效的节点:智能选择时取延迟最小者,否则取选中节点。
+/// 实际生效的节点：同步拉取 AsyncValue；未就绪时取 kDemoNodes 第一条。
 final effectiveNodeProvider = Provider<Node>((ref) {
-  final nodes = ref.watch(nodesProvider);
+  final nodesAsync = ref.watch(nodesProvider);
+  final nodes = nodesAsync.valueOrNull ?? kDemoNodes;
+  if (nodes.isEmpty) return kDemoNodes.first;
+
   final code = ref.watch(selectedNodeCodeProvider);
   if (code == kSmartNodeCode) {
+    // 延迟最小者；MVP 无真实延迟时取第一条
     return nodes.reduce((a, b) => a.ping <= b.ping ? a : b);
   }
   return nodes.firstWhere((n) => n.code == code, orElse: () => nodes.first);