- Remove get_bot_account("qq") fallback from all 4 sender paths
(plan L108/L208/L449: unknown platform = no account, never substitute QQ)
- Sender paths now error immediately if platform bot account is not configured
- Add detailed comments on filter_bot legacy fallback explaining why
global user_id match is needed (plan contingency L528 insufficient for
platform-tagged legacy rows like telegram+qq_account)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
