ci: the packaging test verified a dist the pipeline never built

tests/package-contents.test.ts asserts packages/axis-server/dist/index.js
exists — but axis-server is a standalone npm package, not a bun workspace, so
the root `bun install` never produced it and Axis CI failed on every clean
checkout (every main push since the test landed). Build the package in CI the
same way prepublishOnly does, so the test verifies a real artifact.