Issue with some endpoints #87

My Claude humbly suggested reporting the following:

Bug: /ingest and /contacts endpoints fail on Worker side.

1. contacts.is_mutual NOT NULL violation — listener sends no value, Worker maps to null. Fix: default to 0.
2. ON CONFLICT DO UPDATE duplicate row in batch — retry buffer accumulates dupes. Fix: dedupe by (tg_chat_id, tg_message_id) before UNNEST.