Fix terminal plugin: socket reference, PTY newlines, public mode auth #237

Summary

Three bugs found while testing the --terminal feature (v0.0.118):

1. Socket reference wrong for @fastify/websocket v8+

connection.socket doesn't exist — connection IS the socket in v8+.

// Bug:
const socket = connection.socket;
// Fix:
const socket = connection.socket || connection;

2. Missing carriage returns (newline issue)

Shell output sends \n but xterm.js expects \r\n. Without a real PTY, lines render with staircase indentation.

// Fix: convert \n to \r\n on stdout/stderr output
socket.send(data.toString().replace(/\n/g, '\r\n'));

3. Auth required even on --public servers

The terminal endpoint always requires authentication, even when JSS is started with --public. Should respect the public flag.

4. /bin/sh vs /bin/bash -i

/bin/sh without a PTY doesn't show a prompt. Using /bin/bash -i (interactive mode) provides a prompt and better experience.

Long-term fix

Use node-pty for proper pseudo-terminal support instead of raw child_process.spawn. This would fix newlines, prompt, and interactive program support (vim, top, etc.) properly.