Complete Lab 3 submission

[rslwqr]

Lab 3 — CI/CD

GitHub Actions path

Implemented a PR-gated CI pipeline for QuickNotes with:

• go vet ./...
• go test -race -count=1 ./...
• golangci-lint
• Go 1.23 / 1.24 matrix
• Go module and build caching
• path filtering
• stable CI OK required check
• pinned GitHub Actions and least-privilege permissions

Also completed the bonus CI performance investigation:

• profiled CI step timings
• applied additional workflow optimizations
• compared before/after wall-clock time
• documented the main CI bottlenecks

Full implementation details, measurements, design answers, and evidence are documented in submissions/lab3.md