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/challenges.sql

@@ -19,7 +19,7 @@ CREATE TABLE IF NOT EXISTS t_challenges (
   cta_label VARCHAR(128) NOT NULL COMMENT 'CTA 按钮文字',
   created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
   updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
-) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+) ENGINE=InnoDB 
 
 CREATE TABLE IF NOT EXISTS t_challenge_participants (
   id CHAR(36) NOT NULL PRIMARY KEY,
@@ -36,7 +36,7 @@ CREATE TABLE IF NOT EXISTS t_challenge_participants (
   CONSTRAINT fk_challenge_participant_challenge FOREIGN KEY (challenge_id) REFERENCES t_challenges (id) ON DELETE CASCADE ON UPDATE CASCADE,
   CONSTRAINT fk_challenge_participant_user FOREIGN KEY (user_id) REFERENCES t_users (id) ON DELETE CASCADE ON UPDATE CASCADE,
   CONSTRAINT uq_challenge_participant UNIQUE KEY (challenge_id, user_id)
-) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+) ENGINE=InnoDB 
 
 CREATE INDEX idx_challenge_participants_status_progress
   ON t_challenge_participants (challenge_id, status, progress_value DESC, updated_at ASC);
@@ -53,4 +53,4 @@ CREATE TABLE IF NOT EXISTS t_challenge_progress_reports (
   CONSTRAINT fk_challenge_progress_reports_challenge FOREIGN KEY (challenge_id) REFERENCES t_challenges (id) ON DELETE CASCADE ON UPDATE CASCADE,
   CONSTRAINT fk_challenge_progress_reports_user FOREIGN KEY (user_id) REFERENCES t_users (id) ON DELETE CASCADE ON UPDATE CASCADE,
   CONSTRAINT uq_challenge_progress_reports_day UNIQUE KEY (challenge_id, user_id, report_date)
-) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;
+) ENGINE=InnoDB