Fix stale replyCount in /groups/-/topics due to Redis caching

[Copilot]

/groups/-/topics returns replyCount: 0 for most topics because it fetches topic data via fetchGroupTopicsByIDs(), which caches in Redis with a 24h TTL. Reply counts go stale immediately after caching.

The sibling endpoint /groups/:groupName/topics doesn't have this bug — it queries the DB directly.

• Replace fetcher.fetchGroupTopicsByIDs(tids) with a direct DB query + convert.toGroupTopic(), consistent with how /groups/:groupName/topics already works

// Before: cached, stale replyCount
const topics = await fetcher.fetchGroupTopicsByIDs(tids);

// After: fresh from DB
const topicData = await db
  .select()
  .from(schema.chiiGroupTopics)
  .where(op.inArray(schema.chiiGroupTopics.id, tids));
const topics: Record<number, res.ITopic> = {};
for (const d of topicData) {
  topics[d.id] = convert.toGroupTopic(d);
}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 57.05%. Comparing base (aa0eca1) to head (4a9bf85).
⚠️ Report is 17 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1624      +/-   ##
==========================================
- Coverage   57.29%   57.05%   -0.24%     
==========================================
  Files         151      151              
  Lines        6718     6721       +3     
  Branches     1392     1392              
==========================================
- Hits         3849     3835      -14     
- Misses       2203     2219      +16     
- Partials      666      667       +1     

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