docs(lab4): packet trace, outside-in debugging, and TLS bonus

[selysecr332]

Goal

Lab 4 submission: trace POST /notes with tcpdump, walk an outside-in debug chain on a broken deploy, and decode a TLS handshake (bonus).

Changes

• Added submissions/lab4.md with annotated TCP/HTTP capture, five debug commands, 502 reflection, outside-in chain, and mini-postmortem
• Added submissions/lab4-trace.txt (decoded lab4-trace.pcap excerpt)
• Added submissions/lab4-tls-handshake.txt (openssl ClientHello/ServerHello decode)
• Added app/Caddyfile — HTTPS reverse proxy on :8443 → QuickNotes :8080

Testing

• WSL2: go run ., sudo tcpdump, curl -v POST /notes → 201 Created
• Reproduced bind: address already in use; verified with ss, curl /health, iptables, dig
• Caddy + curl -vk https://localhost:8443/health → TLS 1.3, HTTP 200
• openssl s_client -showcerts and -msg for cert chain + handshake messages

Checklist

• Title is a clear sentence (≤ 70 chars)
• submissions/lab4.md updated
• Task 1 + Task 2 complete
• Bonus TLS handshake documented