Component/runtime specs (*.nuxt.spec.ts) run in the Nuxt environment; all
other specs run in a plain node environment where node_modules stay external,
so native CJS deps like `pg` load correctly (the Nuxt runtime inlines them and
breaks pg's internal `class … extends Pool`). Adds tests/helpers/db.ts, which
spins up and migrates a dedicated test database for repository integration
tests, and renames the board spec to the .nuxt suffix.
