fix(cli): prevent serve crash when port is free on macOS

[prabhtheone]

Summary

Fixes #14800.

On macOS, omniroute serve could crash when the requested port was free.
lsof -ti :PORT exits with code 1 and empty output when no process is
listening, which was incorrectly treated as an unavailable discovery result.

This caused the serve preflight to reach a null value and crash when
accessing .length.

Changes

• Treat lsof exit code 1 with empty output as an empty PID list.
• Preserve null for genuine port-discovery failures.
• Use the existing bind-probe fallback when discovery is unavailable.
• Keep the serve preflight safe when no process is listening.
• Add regression coverage for the macOS lsof no-match case.

Testing

Added a regression test covering:

• macOS lsof returning exit code 1 with empty output.
• Correctly identifying the port as having no listening process.

Related Issue

Closes #14800

[diegosouzapw]

Thanks for chasing #14800 — the exit-code-1-with-empty-stdout case is the real macOS trigger and your test fails without the fix, passes with it. One more piece is needed though: in bin/cli/commands/serve.mjs (lines ~252–264), when discovery returns null and probePortFree() says the port is free, busyPids stays null and busyPids.length throws — that's the crash from the issue for any host without lsof/netstat too. Could you set busyPids = [] in that branch and add a test at the serve level? Happy to merge right after.