feat(client): P4 节点实测延迟/设备/套餐价/兑换/统计接真(#6 6D)

- latency_probe.dart:并行 TCP 握手实测各节点 per-client RTT(服务端无法代知)。
- nodes_provider:解析 /v1/nodes 的 host/port,后台测延迟回填 Node.ping;智能选择
  按实测最小;去掉 8 个伪造演示节点(空列表用中性占位,不再伪造服务器)。
- Node:+host/port/copyWith/pingLabel(未测显示 —);各端 ping 显示改 pingLabel。
- account_screens:PlansScreen 接 /v1/plans(价格 priceLabel + me 标当前档);
  DevicesScreen 接 /v1/me/devices + 移除 DELETE + last_seen;RedeemScreen 接
  /v1/redeem(成功刷新 me,失败显示后端文案)。
- stats_page:周柱接 me.weekly_gb,本月流量/时长接 usage(30),延迟用生效节点实测。
- 顺带补登记早前 log_time.dart 的删除(log.dart 重构遗漏 stage)。

flutter analyze 0 error;115 tests passed;受影响 4 golden 重生成。
本机设备高亮 + 真实 device id 随 P6(device_info_plus)落地。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/state/nodes_provider.dart

@@ -1,49 +1,65 @@
-// nodes_provider.dart — 节点清单 + 当前选择
+// nodes_provider.dart — 节点清单 + 当前选择 + 实测延迟
 //
-// 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。
+// 从 GET /v1/nodes 拉取真实节点(含 host/port);拉取后后台对各节点做 TCP 握手
+// 实测 per-client 延迟并回填。未登录 / 失败返回空列表(不再伪造演示节点)。
+import 'dart:async';
 import 'dart:convert';
 
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:http/http.dart' as http;
 
 import '../models/node.dart';
+import '../services/api_config.dart';
+import '../services/latency_probe.dart';
 import 'auth_provider.dart';
 
-// ── 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>> {
+  bool _disposed = false;
+
   @override
   Future<List<Node>> build() async {
+    ref.onDispose(() => _disposed = true);
     final auth = ref.watch(authProvider);
-    if (!auth.isLoggedIn) return kDemoNodes;
-    return _fetchNodes(auth.accessToken!);
+    if (!auth.isLoggedIn) return const [];
+    final list = await _fetchNodes(auth.accessToken!);
+    unawaited(_measure(list));
+    return list;
   }
 
   Future<void> refresh() async {
-    state = const AsyncLoading();
     final auth = ref.read(authProvider);
     if (!auth.isLoggedIn) {
-      state = AsyncData(kDemoNodes);
+      state = const AsyncData([]);
       return;
     }
-    state = await AsyncValue.guard(() => _fetchNodes(auth.accessToken!));
+    state = const AsyncLoading();
+    state = await AsyncValue.guard(() async {
+      final list = await _fetchNodes(auth.accessToken!);
+      unawaited(_measure(list));
+      return list;
+    });
+  }
+
+  /// 后台实测各节点延迟,完成后回填(notifier 未销毁才更新)。
+  Future<void> _measure(List<Node> list) async {
+    if (list.isEmpty) return;
+    final pings = await probeAll(
+      [for (final n in list) (uuid: n.uuid, host: n.host, port: n.port)],
+    );
+    if (_disposed) return;
+    final updated = [for (final n in list) n.copyWith(ping: pings[n.uuid] ?? n.ping)];
+    state = AsyncData(updated);
   }
 
   static Future<List<Node>> _fetchNodes(String accessToken) async {
-    final uri = Uri.parse('$_kApiUrl/v1/nodes');
+    final uri = Uri.parse('$kApiBaseUrl/v1/nodes');
     final resp = await http.get(uri, headers: {
       'Authorization': 'Bearer $accessToken',
     }).timeout(const Duration(seconds: 10));
 
-    if (resp.statusCode != 200) return kDemoNodes;
+    if (resp.statusCode != 200) return const [];
 
     final body = jsonDecode(resp.body) as Map<String, dynamic>;
     final rawList = body['nodes'] as List<dynamic>? ?? [];
@@ -55,7 +71,9 @@ class NodesNotifier extends AsyncNotifier<List<Node>> {
         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
+        host: m['host'] as String? ?? '',
+        port: (m['port'] as num?)?.toInt() ?? 0,
+        ping: 0, // 由 _measure 实测回填
       );
     }).toList();
   }
@@ -64,7 +82,7 @@ class NodesNotifier extends AsyncNotifier<List<Node>> {
 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);
 
@@ -73,16 +91,18 @@ final isSmartSelectProvider = Provider<bool>(
   (ref) => ref.watch(selectedNodeCodeProvider) == kSmartNodeCode,
 );
 
-/// 实际生效的节点：同步拉取 AsyncValue；未就绪时取 kDemoNodes 第一条。
+/// 实际生效的节点:列表为空时返回占位;智能选择取实测延迟最小者(未测得排后)。
 final effectiveNodeProvider = Provider<Node>((ref) {
-  final nodesAsync = ref.watch(nodesProvider);
-  final nodes = nodesAsync.valueOrNull ?? kDemoNodes;
-  if (nodes.isEmpty) return kDemoNodes.first;
+  final nodes = ref.watch(nodesProvider).valueOrNull ?? const <Node>[];
+  if (nodes.isEmpty) return kPlaceholderNode;
 
   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.reduce((a, b) {
+      final pa = a.ping > 0 ? a.ping : 1 << 30;
+      final pb = b.ping > 0 ? b.ping : 1 << 30;
+      return pa <= pb ? a : b;
+    });
   }
   return nodes.firstWhere((n) => n.code == code, orElse: () => nodes.first);
 });