feat: 用户管理对接真实 API

后端: 新增 /api/v1/users CRUD + 重置密码接口
前端: user model/repository/provider + 设置页用户 tab 改为真实数据，
      支持新增、编辑、启停、重置密码

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

client/lib/models/user.dart

@@ -0,0 +1,42 @@
+class AppUser {
+  final int id;
+  final String username;
+  final String? realName;
+  final String? phone;
+  final String role; // admin | operator | readonly
+  final bool isActive;
+  final String? createdAt;
+
+  const AppUser({
+    required this.id,
+    required this.username,
+    this.realName,
+    this.phone,
+    required this.role,
+    required this.isActive,
+    this.createdAt,
+  });
+
+  String get roleLabel {
+    switch (role) {
+      case 'admin':
+        return '管理员';
+      case 'operator':
+        return '操作员';
+      case 'readonly':
+        return '只读';
+      default:
+        return role;
+    }
+  }
+
+  factory AppUser.fromJson(Map<String, dynamic> json) => AppUser(
+        id: (json['id'] as num).toInt(),
+        username: json['username'] as String,
+        realName: json['real_name'] as String?,
+        phone: json['phone'] as String?,
+        role: json['role'] as String? ?? 'operator',
+        isActive: json['is_active'] as bool? ?? true,
+        createdAt: json['created_at'] as String?,
+      );
+}