Prevent infinite loops by tracking processed message IDs in WhatsApp
channel. The bridge may send duplicate messages which caused the bot
to respond repeatedly with the same generic message.
Changes:
- Add _processed_message_ids deque (max 2000) to track seen messages
- Skip processing if message_id was already processed
- Align WhatsApp dedup with other channels (Feishu, Email, Mochat, QQ)
This fixes the issue where WhatsApp gets stuck in a loop sending
identical responses repeatedly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
