fix(bugcollect): 修复 trend 接口 500 — GROUP BY 兼容 MySQL only_full_group_by

SELECT e.createdAt 配合 GROUP BY DATE(e.createdAt) 在 MySQL strict mode
下触发 Expression #1 of SELECT list is not in GROUP BY clause 错误。
改为 MIN(e.createdAt) 作为聚合列，类型不变，LogService 无需修改。

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

xuqm-bugcollect-service/src/main/java/com/xuqm/bugcollect/repository/LogIssueEventRepository.java

@@ -25,7 +25,7 @@ public interface LogIssueEventRepository extends JpaRepository<LogIssueEventEnti
     Page<LogIssueEventEntity> findByAppKeyAndCreatedAtBetween(
             String appKey, LocalDateTime from, LocalDateTime to, Pageable pageable);
 
-    @Query("SELECT e.createdAt, COUNT(e), COUNT(DISTINCT e.userId) FROM LogIssueEventEntity e " +
+    @Query("SELECT MIN(e.createdAt), COUNT(e), COUNT(DISTINCT e.userId) FROM LogIssueEventEntity e " +
            "WHERE e.issueId = :issueId AND e.createdAt BETWEEN :from AND :to " +
            "GROUP BY FUNCTION('DATE', e.createdAt) ORDER BY FUNCTION('DATE', e.createdAt)")
     List<Object[]> findDailyCountsByIssueId(