feat(client): P1 真实数据接入地基(#6 6A)

- api_config.dart:API 基址单源(消除各处重复 _kApiUrl)
- api_client.dart:统一鉴权 HTTP 客户端,401→AuthNotifier.refresh→重试一次,
  错误统一 AuthApiException;+ 单测覆盖 401 刷新重试
- 模型 me/device/plan/usage_point(对齐后端 snake_case 契约)
- account_api.dart:/v1/me、/v1/plans、/v1/me/devices(列表+删)、/v1/usage、
  /v1/redeem、/v1/ads/unlock 封装
- auth_provider:注入 AuthApi + refresh();account_providers 装配 ApiClient/AccountApi
- 顺带修复 onboarding 提交遗留的测试 stub(_NullTokenStore 缺 isOnboarded/markOnboarded)

flutter analyze 0 error;114 tests passed。

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

client/lib/models/me.dart

@@ -0,0 +1,60 @@
+// me.dart — 当前账户聚合视图(GET /v1/me)。
+//
+// 一发覆盖账号/套餐/配额/今日+周流量,对齐后端契约
+// (server/internal/httpapi/account.go + web/usercenter http.ts)。
+
+/// 账户档案。字段对齐后端 snake_case JSON。
+class Me {
+  const Me({
+    required this.email,
+    required this.plan,
+    this.expiresAt,
+    this.devicesUsed = 0,
+    this.devicesMax = 1,
+    this.quotaTodayMin,
+    this.dataTodayGb = 0,
+    this.weeklyGb = const [],
+    this.totpEnabled = false,
+  });
+
+  final String email;
+
+  /// 'free' | 'pro' | 'team'。
+  final String plan;
+
+  /// 订阅到期(UTC);免费版/无订阅为 null。
+  final DateTime? expiresAt;
+
+  final int devicesUsed;
+  final int devicesMax;
+
+  /// 今日额度上限(分钟);null = 不限(pro/team)。
+  final int? quotaTodayMin;
+
+  /// 今日已用流量(GB)。
+  final double dataTodayGb;
+
+  /// 近 7 天每日流量(GB),旧→新。
+  final List<double> weeklyGb;
+
+  final bool totpEnabled;
+
+  bool get isFree => plan == 'free';
+
+  factory Me.fromJson(Map<String, dynamic> m) {
+    final exp = (m['expires_at'] ?? m['expire_at']) as String?;
+    return Me(
+      email: m['email'] as String? ?? '',
+      plan: m['plan'] as String? ?? 'free',
+      expiresAt: (exp != null && exp.isNotEmpty) ? DateTime.tryParse(exp) : null,
+      devicesUsed: (m['devices_used'] as num?)?.toInt() ?? 0,
+      devicesMax: (m['devices_max'] as num?)?.toInt() ?? 1,
+      quotaTodayMin: (m['quota_today_min'] as num?)?.toInt(),
+      dataTodayGb: (m['data_today_gb'] as num?)?.toDouble() ?? 0,
+      weeklyGb: ((m['weekly_gb'] as List<dynamic>?) ?? const [])
+          .map((e) => (e as num).toDouble())
+          .toList(),
+      totpEnabled: m['totp_enabled'] as bool? ?? false,
+    );
+  }
+}