fix(npm): install musl binaries on Linux and surface binary crashes

[bntvllnt]

Fixes #998.

Problem

When installed via npm on some Linux hosts, railway login --browserless (and in fact every network command) exits 1 with no output. The reporter saw a silent failure inside a TTY, which looked like a TTY-detection bug but is actually two stacked defects in the npm distribution channel.

Root cause

1. npm ships the gnu binary on Linux, which can crash.
npm-install/postinstall.js resolves the download target via @napi-rs/triples, whose first Linux entry is the *-unknown-linux-gnu triple. On some Linux hosts that binary hits a general protection fault in vendored crypto during the TLS key exchange, so it dies with SIGSEGV on the first network call:

traps: railway[…] general protection fault … in railway[…]

The musl binary built from the same source works on the same host. This is also why install.sh already prefers musl on Linux:

# use the statically compiled musl bins on linux to avoid linking issues.
linux) platform="unknown-linux-musl" ;;

The gnu-first ordering has two more consequences: npm installs 404 on aarch64 and arm Linux, because only musl assets are published for those architectures.

2. The bin wrapper hides the crash.
bin/railway.js ran the binary and collapsed any failure into exit(1), discarding both the crash signal and the binary's real exit code — turning the segfault into a silent exit 1.

Changes

File	Change
npm-install/postinstall.js	Resolve Linux targets through an explicit musl map matching the published release assets. Other platforms keep the existing triples lookup.
bin/railway.js	Print an actionable message when the binary is killed by a signal, and propagate the binary's real exit code instead of always 1.

Two files, one hunk each. No Rust/binary changes.

Testing

Verified on an affected Linux host by installing this branch as the global package:

• postinstall now downloads …-x86_64-unknown-linux-musl.tar.gz; the resulting binary is static-pie/musl.
• railway login --browserless (the exact railway login --browserless exits silently in TTY on Linux #998 repro, in a TTY) now prints the device-code sign-in flow and polls, instead of exiting 1 silently.
• Exit codes propagate: an unknown subcommand returns 2 (was 1); an unauthenticated whoami returns a clean 1 (was SIGSEGV/139).
• Wrapper matrix (stub binaries): exit 0 → 0, exit 2 → 2, SIGSEGV → actionable message + 1.
• Target map resolves to a published asset for every Linux arch (x64, arm64, ia32, arm); darwin/win32 unchanged.

Notes

• Suggested release label: release/patch — the fix reaches users through a version bump on npm.
• A separate follow-up may be worth opening for why the gnu artifact faults (toolchain/CPU baseline), so the gnu build can either be repaired or dropped from the published matrix. This PR removes user impact by not shipping it to npm Linux users, matching install.sh.