Opt query activities

[AlexCXC]

No description provided.

[seafile-dev]

Verdict: Request changes

Blocking:

• The activity-day boundary and cache key are wrong for offsets with non-zero minutes; see the inline comment.

Warnings:

• No regression coverage was added for cache hit/miss behavior, empty historical days, the current-day bypass, or minute-offset zones.
  Suggested fix: add focused unit tests around the day-range/query helpers and a Redis stub covering +05:30 and -03:30, including an instant that crosses the requested local midnight.

[seafile-dev]

[Critical] 分钟级时区被忽略

Why this matters:
to_tz 来自前端的 dayjs().format().slice(-6)，会包含如 +05:30 的有效偏移；这里仅使用小时构造 Etc/GMT，完全丢弃分钟。比如 UTC 18:45 在 +05:30 已是次日 00:15，但实现仍按 +05:00 归到前一天，因此查询范围、返回日期和 Redis key 都会落在错误的自然日，并会把错误统计缓存 24 小时。

Suggested fix: 解析并保留 hours 和 minutes，使用 pytz.FixedOffset(sign * (hours * 60 + minutes))（或等价的固定偏移 tzinfo），并补充跨本地午夜的 +05:30/负分钟偏移回归测试。