Implement QQ Official messaging channel using OAuth2 authentication
with Discord-like WebSocket gateway protocol for events.
- Add QQChannel with send/listen/health_check support
- Add QQConfig (app_id, app_secret, allowed_users)
- OAuth2 token refresh and WebSocket heartbeat management
- Message deduplication with capacity-based eviction
- Support both C2C (private) and group AT messages
- Integrate with onboard wizard, integrations registry, and channel
list/doctor commands
- Include unit tests for user allowlist, deduplication, and config
