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

sql-scripts/fix-collation.sql

@@ -0,0 +1,41 @@
+-- 修复字符集排序规则不一致的问题
+-- 将所有相关表的字符集统一为 utf8mb4_unicode_ci
+
+-- 检查当前表的字符集和排序规则
+SELECT 
+    TABLE_NAME,
+    TABLE_COLLATION,
+    CHARACTER_SET_NAME
+FROM INFORMATION_SCHEMA.TABLES 
+WHERE TABLE_SCHEMA = DATABASE() 
+AND TABLE_NAME IN ('t_users', 't_challenge_participants', 't_challenges');
+
+-- 检查列的字符集和排序规则
+SELECT 
+    TABLE_NAME,
+    COLUMN_NAME,
+    COLLATION_NAME,
+    CHARACTER_SET_NAME
+FROM INFORMATION_SCHEMA.COLUMNS 
+WHERE TABLE_SCHEMA = DATABASE() 
+AND TABLE_NAME IN ('t_users', 't_challenge_participants', 't_challenges')
+AND COLUMN_NAME IN ('id', 'user_id', 'challenge_id');
+
+-- 修改表字符集和排序规则
+ALTER TABLE t_users CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+ALTER TABLE t_challenge_participants CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+ALTER TABLE t_challenges CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+
+-- 修改特定列的字符集和排序规则（如果需要）
+ALTER TABLE t_users MODIFY id VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+ALTER TABLE t_challenge_participants MODIFY user_id VARCHAR(64) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+ALTER TABLE t_challenge_participants MODIFY challenge_id CHAR(36) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
+
+-- 验证修复结果
+SELECT 
+    TABLE_NAME,
+    TABLE_COLLATION,
+    CHARACTER_SET_NAME
+FROM INFORMATION_SCHEMA.TABLES 
+WHERE TABLE_SCHEMA = DATABASE() 
+AND TABLE_NAME IN ('t_users', 't_challenge_participants', 't_challenges');