docs(lab4): trace POST /notes, outside-in debug, TLS handshake

[markovav-official]

Goal

Document end-to-end tracing of POST /notes on a Linux VM using tcpdump, substrate debug tools, and a TLS-terminated Caddy proxy.

Changes

• submissions/lab4.md — Task 1 (packet capture + 5 commands + 502 reflection), Task 2 (bind conflict + outside-in chain + postmortem), Bonus (TLS 1.3 handshake decode)
• submissions/attachments/lab4/ — lab4-trace.pcap/.txt, debug-commands.txt, task2-broken.txt, lab4-tls.pcap, ClientHello/ServerHello/openssl dumps

Testing

• Ubuntu 24.04 VM capstone55: QuickNotes on :8080, curl -v POST /notes → 201 Created
• Task 2: reproduced listen tcp :8080: bind: address already in use, repaired after killing conflicting PID
• Bonus: curl -vk https://localhost:8443/health → TLS 1.3, HTTP 200 via Caddy reverse proxy

Checklist

• Title is a clear sentence (≤ 70 chars)
• Commits are signed (git log --show-signature)
• submissions/lab4.md updated