The _send_qqbot function was hardcoded to use the guild channel
endpoint (/channels/{id}/messages), which fails for C2C private
chats and QQ groups with 'channel does not exist' (code 11263).
This change tries the appropriate endpoints in order:
1. /channels/{id}/messages (guild channels)
2. /v2/users/{id}/messages (C2C private chats)
3. /v2/groups/{id}/messages (QQ groups)
Fixes active sending to QQBot C2C and group recipients.