Implement Lab 6 containerization and hardening for QuickNotes

[smairon]

Goal

Complete Lab 6 for QuickNotes: containerize the app, run it with Compose and persistence, and apply the bonus hardening defaults.

Changes

• Task 1:
  Add a multi-stage distroless Dockerfile with a static stripped Go binary, nonroot runtime, and image size under 25 MB.
• Task 2:
  Add compose.yaml with port publishing, named volume persistence, env vars, restart policy, and a distroless-compatible healthcheck.
• Bonus:
  Harden the quicknotes service with cap_drop: [ALL], read_only: true, tmpfs: /tmp, and no-new-privileges; document Docker and Trivy verification in submissions/lab6.md.

Testing

• go test ./...
• docker build -t quicknotes:lab6 ./app
• docker run --rm -p 8080:8080 -v "$PWD/app/data:/data" quicknotes:lab6 and curl /health
• docker compose up --build -d, POST note, verify persistence across down/up, verify reset with down -v
• docker inspect checks for nonroot, dropped capabilities, read-only root, and no-new-privileges
• docker compose exec quicknotes sh fails as expected
• trivy image --severity HIGH,CRITICAL quicknotes:lab6

Checklist

• Title is a clear sentence (≤ 70 chars)
• Commits are signed (git log --show-signature)
• submissions/lab6.md updated