feat(challenges): 新增挑战功能模块及完整接口实现

- 新增挑战列表、详情、加入/退出、进度上报等 REST 接口
- 定义 Challenge / ChallengeParticipant 数据模型与状态枚举
- 提供排行榜查询与用户排名计算
- 包含接口文档与数据库初始化脚本

src/challenges/models/challenge.model.ts

@@ -0,0 +1,123 @@
+import { Table, Column, DataType, Model, HasMany } from 'sequelize-typescript';
+import { ChallengeParticipant } from './challenge-participant.model';
+
+export enum ChallengeStatus {
+  UPCOMING = 'upcoming',
+  ONGOING = 'ongoing',
+  EXPIRED = 'expired',
+}
+
+@Table({
+  tableName: 't_challenges',
+  underscored: true,
+})
+export class Challenge extends Model {
+  @Column({
+    type: DataType.CHAR(36),
+    defaultValue: DataType.UUIDV4,
+    primaryKey: true,
+  })
+  declare id: string;
+
+  @Column({
+    type: DataType.STRING(255),
+    allowNull: false,
+    comment: '挑战标题',
+  })
+  declare title: string;
+
+  @Column({
+    type: DataType.STRING(512),
+    allowNull: true,
+    comment: '挑战封面图',
+  })
+  declare image: string;
+
+  @Column({
+    type: DataType.DATE,
+    allowNull: false,
+    comment: '挑战开始时间',
+  })
+  declare startAt: Date;
+
+  @Column({
+    type: DataType.DATE,
+    allowNull: false,
+    comment: '挑战结束时间',
+  })
+  declare endAt: Date;
+
+  @Column({
+    type: DataType.STRING(128),
+    allowNull: true,
+    comment: '周期标签，例如「21天挑战」',
+  })
+  declare periodLabel: string | null;
+
+  @Column({
+    type: DataType.STRING(128),
+    allowNull: false,
+    comment: '持续时间标签，例如「持续21天」',
+  })
+  declare durationLabel: string;
+
+  @Column({
+    type: DataType.STRING(255),
+    allowNull: false,
+    comment: '挑战要求标签，例如「每日练习 1 次」',
+  })
+  declare requirementLabel: string;
+
+  @Column({
+    type: DataType.TEXT,
+    allowNull: true,
+    comment: '挑战概要说明',
+  })
+  declare summary: string | null;
+
+  @Column({
+    type: DataType.INTEGER,
+    allowNull: false,
+    comment: '挑战目标值（例如需要完成的天数）',
+  })
+  declare targetValue: number;
+
+  @Column({
+    type: DataType.STRING(64),
+    allowNull: false,
+    defaultValue: '天',
+    comment: '进度单位，用于展示排行榜指标',
+  })
+  declare progressUnit: string;
+
+  @Column({
+    type: DataType.STRING(255),
+    allowNull: true,
+    comment: '排行榜描述，例如「连续打卡榜」',
+  })
+  declare rankingDescription: string | null;
+
+  @Column({
+    type: DataType.STRING(255),
+    allowNull: false,
+    comment: '高亮标题',
+  })
+  declare highlightTitle: string;
+
+  @Column({
+    type: DataType.STRING(255),
+    allowNull: false,
+    comment: '高亮副标题',
+  })
+  declare highlightSubtitle: string;
+
+  @Column({
+    type: DataType.STRING(128),
+    allowNull: false,
+    comment: 'CTA 按钮文字',
+  })
+  declare ctaLabel: string;
+
+  @HasMany(() => ChallengeParticipant)
+  declare participants?: ChallengeParticipant[];
+}