Add delivery confirmation and read receipts for private messages

- Implement full delivery status flow: sending → sent → delivered → read
- Add visual indicators (gray/green/blue checkmarks) 
- Create DeliveryTracker service for managing confirmations
- Add end-to-end encrypted ACK and read receipt messages
- Handle ephemeral peer ID changes with message migration
- Fix message ID preservation in BinaryProtocol
- Ensure proper delivery status for incoming messages
- Add multiple triggers for sending read receipts
- Maintain full backwards compatibility with older clients

Visual indicators:
- ○ Gray circle = Sending
- ✓ Gray check = Sent
- ✓✓ Green double checks = Delivered  
- ✓✓ Blue double checks = Read
- ⚠ Red triangle = Failed