docs(lab4): submit network debugging evidence

[IlyaPechersky]

Goal

Submit Lab 4 requirements.

Changes

• Added submissions/lab4.md with packet trace, outside-in debugging, and TLS bonus evidence
• Added HTTP and TLS packet capture artifacts under lab4-artifacts/
• Documented macOS equivalents for Linux-only commands where needed

Testing

• Captured and decoded a POST /notes request with tcpdump
• Reproduced bind: address already in use and repaired it
• Captured TLS handshake through local Caddy reverse proxy

Checklist

• Title is a clear sentence (<= 70 chars)
• Commits are signed (git log --show-signature)
• submissions/labN.md updated