fix(server): 修复群组权限缓存与解散群问题

1. 新增group事件处理逻辑，实时刷新内存中的群组权限与状态
2. 加载topic时过滤已解散的群组，防止被旧成员恢复
3. 补充群成员离开事件的用户ID字段，完善事件处理

server/store/store.go

@@ -1743,6 +1743,11 @@ func (groupBusinessMapper) Dissolve(tenantID types.TenantID, topic string, actor
 		invalidateGroupMemberPages(tenantID, topic)
 		invalidateGroupMemberObjects(tenantID, topic)
 		invalidateTopicSubscriptions(tenantID, topic)
+		// The dissolve flips im_topics.state to StateDeleted. The cached topic
+		// object must be dropped too, otherwise a later Topics.Get (e.g. from
+		// initTopicGrp when a former member re-subscribes) would restore the
+		// dissolved group from the stale cache.
+		_ = DeleteCachedObject(tenantID, cacheNamespaceTopic, strings.TrimSpace(topic))
 	}
 	return settings, err
 }
@@ -2132,6 +2137,9 @@ func (groupBusinessMapper) TransferOwner(tenantID types.TenantID, topic string,
 		_ = DeleteCachedObject(tenantID, cacheNamespaceSub, subscriptionCacheID(topic, uid, false))
 		_ = DeleteCachedObject(tenantID, cacheNamespaceSub, subscriptionCacheID(topic, uid, true))
 	}
+	// im_topics.owner is updated by the transfer; drop the cached topic
+	// object so a later Topics.Get sees the new owner.
+	_ = DeleteCachedObject(tenantID, cacheNamespaceTopic, topic)
 	invalidateGroupMemberPages(tenantID, topic)
 	return nil
 }