Add a proper build step (dummy `build` is a temporary CI stopgap)

[Shinrai]

What / why

The @v4 CI coverage-badge leg runs coverage_build_command (default npm run build) before computing coverage. This repo has no build step, so the PR Coverage Badge check failed on release PR #3 with npm error Missing script: "build". Coverage itself is fine — real ci:coverage + a json-summary reporter — so the badge stays enabled.

Stopgap in place (commit 8eb47b7 on next)

A dummy no-op build so npm run build exits 0:

"build": "echo 'no build step - stopgap for CI coverage-badge; see tracking issue'"

This is temporary.

The real work — give this repo a proper build

This repo already has a real build:ci (npm run lint && npm run format:check && npm run types:build). The right resolution is to make the coverage leg use it — set coverage_build_command: "npm run build:ci" in the workflow-ci.yml caller (or wire a dedicated build) — then drop the dummy build. skip_build: true is the fallback if a build genuinely isn't wanted for coverage.

Not an upstream issue

CLDMV/.github's @v4 already honors skip_build and coverage_build_command end-to-end (both coverage jobs thread them through) — no .github change is needed. This is purely a per-repo build-setup task.