fix(db): 统一字符集排序规则并修复时间戳类型

- 新增 SQL 脚本统一表与列字符集为 utf8mb4_unicode_ci
- 移除建表语句冗余 COLLATE 子句，由全局配置控制
- 将挑战起止时间字段由 Date 改为 BIGINT 时间戳，避免时区与精度问题
- 补充 Winston 日志追踪挑战详情查询性能
- 数据库模块新增 charset 与 collate 全局配置，确保后续表一致性

BREAKING CHANGE: challenge.startAt/endAt 由 Date 变更为 number(毫秒时间戳)，调用方需同步调整类型

src/challenges/challenges.service.ts

@@ -1,4 +1,4 @@
-import { Injectable, NotFoundException, BadRequestException, ConflictException } from '@nestjs/common';
+import { Injectable, NotFoundException, BadRequestException, ConflictException, Inject } from '@nestjs/common';
 import { InjectModel } from '@nestjs/sequelize';
 import { Challenge, ChallengeStatus } from './models/challenge.model';
 import { ChallengeParticipant, ChallengeParticipantStatus } from './models/challenge-participant.model';
@@ -10,10 +10,15 @@ import { ChallengeProgressDto, RankingItemDto } from './dto/challenge-progress.d
 import { fn, col, Op, UniqueConstraintError } from 'sequelize';
 import * as dayjs from 'dayjs';
 import { User } from '../users/models/user.model';
+import { WINSTON_MODULE_PROVIDER } from 'nest-winston';
+import { Logger as WinstonLogger } from 'winston';
 
 @Injectable()
 export class ChallengesService {
+
   constructor(
+    @Inject(WINSTON_MODULE_PROVIDER) private readonly winstonLogger: WinstonLogger,
+
     @InjectModel(Challenge)
     private readonly challengeModel: typeof Challenge,
     @InjectModel(ChallengeParticipant)
@@ -100,6 +105,13 @@ export class ChallengesService {
       throw new NotFoundException('挑战不存在');
     }
 
+    this.winstonLogger.info('start get detail', {
+      context: 'getChallengeDetail',
+      userId,
+      challengeId,
+    });
+
+
     const [participantsCount, participation] = await Promise.all([
       this.participantModel.count({
         where: {
@@ -118,6 +130,15 @@ export class ChallengesService {
       }),
     ]);
 
+    this.winstonLogger.info('end get detail', {
+      context: 'getChallengeDetail',
+      userId,
+      challengeId,
+      participantsCount,
+      participation,
+    });
+
+
     const rankingsRaw = await this.participantModel.findAll({
       where: {
         challengeId,
@@ -131,6 +152,15 @@ export class ChallengesService {
       limit: 10,
     });
 
+    this.winstonLogger.info('get rankingsRaw end', {
+      context: 'getChallengeDetail',
+      userId,
+      challengeId,
+      participantsCount,
+      participation,
+      rankingsRawCount: rankingsRaw.length,
+    });
+
     const progress = participation
       ? this.buildChallengeProgress(participation.progressValue, participation.targetValue, challenge.progressUnit)
       : undefined;
@@ -333,7 +363,7 @@ export class ChallengesService {
     };
   }
 
-  private computeStatus(startAt: Date, endAt: Date): ChallengeStatus {
+  private computeStatus(startAt: number, endAt: number): ChallengeStatus {
     const now = dayjs();
     const start = dayjs(startAt);
     const end = dayjs(endAt);