feat(test): WP-46 — Vitest coverage (report-only)

Enable coverage via the @angular/build:unit-test builder's first-class options: a
`coverage` configuration on the test target (v8 provider, text-summary/html/lcov,
excludes for specs/stories/contracts/generated client) + `npm run test:coverage`.
Report-only (no thresholds) — visibility first. CI's test step now runs test:coverage
(strict superset: fails on a failing test, never on coverage). Baseline ~71% stmts.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/ci-local.sh

@@ -15,7 +15,7 @@ step "lint";                      npm run lint
 step "dependency boundaries";     npm run dep:check
 step "format:check (prettier)";   npm run format:check
 step "check:tokens";              npm run check:tokens
-step "test (vitest)";             npm test
+step "test (vitest + coverage)";  npm run test:coverage
 step "build --localize (nl+en)";  npx ng build --localize
 step "npm audit (shipped deps)";  npm audit --omit=dev
 step "backend format + tests";    ( cd backend && dotnet format BigRegister.slnx --verify-no-changes && dotnet test BigRegister.slnx )