Critical fixes:
1. Match messages by sender nickname in addition to peer ID (since peer IDs change)
2. Send read receipts to CURRENT peer ID, not old senderPeerID from message
3. Remove requirement for senderPeerID to be non-nil (blocks older messages)
4. Add extensive logging to trace the flow
The core issue was that peer IDs are ephemeral and change between sessions:
- Rick sends message with peer ID A
- Later, Jack connects to Rick who now has peer ID B
- Read receipt needs to be sent to B, not A
- Messages need to be matched by nickname, not just peer ID
