Specs truncate the test DB between tests; with multiple DB-backed spec files
running in parallel workers they clobbered each other. Suffix the database
name with VITEST_POOL_ID so each worker is isolated.
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.
