Missing error handling in message receive loop

[rafabd1]

In receive_loop() (session.rs:434-450), errors are silently logged but the stream is just closed:

match read_framed(&mut reader).await {
    Ok(frame) => {
        if let Err(e) = handle_incoming_message(&app, &frame).await {
        }
    }
    Err(e) => {
        *state.session.lock().await = None;
        let _ = app.emit("session_closed", ());
    }
}

Problems:

1. Individual message errors don't close session: If one message fails to decrypt/process, the loop continues but the peer may have sent a critical message
2. No user notification: User doesn't know there was an error. Messages may appear to not be received.
3. Decryption errors silently ignored: Could indicate:
   • Ratchet desynchronization (key mismatch)
   • Peer sent malformed data
   • Network corruption
   • Active attack (?)

Examples:

• Peer sends message with counter=2, but we expected counter=1
• Ratchet.decrypt() fails but we ignore it and keep the stream open
• Later messages (counter=3,4,...) also fail, but user has no idea

Proposed solution:

• Treat decryption errors as fatal (close session, show user "decryption failed")
• Log failures with more context (counter, error type)
• Show user a warning: "Lost sync with peer, please reconnect"