orly-repl: piped-stdin EOF aborts in-flight entries and process.exit truncates their output #542

Found by #539's docker gate (printf '40 + 2;\n:quit\n' | docker run -i ... repl printed no result and exited 0), reproduced outside docker — any piped, non-interactive use hits it:

printf '40 + 2;\n' | orly-repl ...   # banner, one prompt, silence, exit 0

Two defects compound:

1. EOF races the entry queue. Line handlers are serialized on a promise chain, but readline's close (stdin EOF) handler calls quit() immediately — closing the WebSocket and deleting the scratch dir while the first entry is still compiling/installing. The entry's rejection lands in the chain after quitting is set, and its prompt/result never print.
2. process.exit(0) truncates pending pipe writes. The aborted entry's error text goes to stderr via console.error, whose write to a pipe is asynchronous; process.exit drops it. So the failure is silent — exit 0, no output — which is what made the CI log useless (11s of work, then nothing).

Fix: chain quit() onto the entry queue so EOF means "quit after pending entries drain" (interactive :quit/Ctrl-D semantics unchanged), and replace process.exit(0) with process.exitCode + natural event-loop drain so output always flushes. The smoke gains a piped-EOF scenario (lines written, stdin closed immediately — the exact CI shape).