feat(challenges): 接入真实接口并完善挑战列表与详情状态管理

- 新增 challengesApi 服务层，支持列表/详情/加入/退出/打卡接口
- 重构 challengesSlice，使用 createAsyncThunk 管理异步状态
- 列表页支持加载、空态、错误重试及状态标签
- 详情页支持进度展示、打卡、退出及错误提示
- 统一卡片与详情数据模型，支持动态状态更新

services/challengesApi.ts

@@ -0,0 +1,65 @@
+import { api } from './api';
+
+export type ChallengeStatus = 'upcoming' | 'ongoing' | 'expired';
+
+export type ChallengeProgressDto = {
+  completed: number;
+  target: number;
+  remaining: number;
+  badge: string;
+  subtitle?: string;
+};
+
+export type RankingItemDto = {
+  id: string;
+  name: string;
+  avatar: string | null;
+  metric: string;
+  badge?: string;
+};
+
+export type ChallengeListItemDto = {
+  id: string;
+  title: string;
+  image: string;
+  periodLabel?: string;
+  durationLabel: string;
+  requirementLabel: string;
+  status: ChallengeStatus;
+  participantsCount: number;
+  rankingDescription?: string;
+  highlightTitle: string;
+  highlightSubtitle: string;
+  ctaLabel: string;
+  progress?: ChallengeProgressDto;
+  isJoined: boolean;
+  startAt?: string;
+  endAt?: string;
+};
+
+export type ChallengeDetailDto = ChallengeListItemDto & {
+  summary?: string;
+  rankings: RankingItemDto[];
+  userRank?: number;
+};
+
+export async function listChallenges(): Promise<ChallengeListItemDto[]> {
+  return api.get<ChallengeListItemDto[]>('/challenges');
+}
+
+export async function getChallengeDetail(id: string): Promise<ChallengeDetailDto> {
+  return api.get<ChallengeDetailDto>(`/challenges/${encodeURIComponent(id)}`);
+}
+
+export async function joinChallenge(id: string): Promise<ChallengeProgressDto> {
+  return api.post<ChallengeProgressDto>(`/challenges/${encodeURIComponent(id)}/join`);
+}
+
+export async function leaveChallenge(id: string): Promise<boolean> {
+  return api.post<boolean>(`/challenges/${encodeURIComponent(id)}/leave`);
+}
+
+export async function reportChallengeProgress(id: string, increment?: number): Promise<ChallengeProgressDto> {
+  const body = increment != null ? { increment } : undefined;
+  return api.post<ChallengeProgressDto>(`/challenges/${encodeURIComponent(id)}/progress`, body);
+}