ci: add GitHub Actions pipeline (tsc + lint + test + coverage gate)

[marcuspat]

v1.1.0 target

NOIP has no CI pipeline in v1.0.0. Add a GitHub Actions workflow that enforces the full validation gate on every PR and push to main.

Scope:

• .github/workflows/ci.yml — triggered on push/PR to main
• Jobs: typecheck → lint → test (with coverage gate) → build
• Matrix: Node 22 LTS
• Cache: npm ci with node_modules cache
• Services: MongoDB and Redis containers for integration tests

Workflow gates (must all pass):

tsc --noEmit          # 0 errors
eslint . --ext .ts    # 0 errors
jest --coverage       # 0 failures, ≥80% coverage (v1.1.0 threshold)
tsc                   # build exits 0

Acceptance criteria:

• PR badge shows CI status in README
• Merges to main blocked if any gate fails
• Pipeline runs in < 5 minutes on a standard GitHub runner

Context: v1.0.0 release notes list this as the first v1.1.0 target. Validation commands are already defined in package.json scripts.