config.ts requires JWT_SECRET at module-load time. Since `.env` is gitignored
it doesn't propagate to git worktrees, fresh clones, or CI without secrets —
producing 200+ confusing cascade failures (vitest module-mock errors that
look unrelated to the real cause).
Add a vitest setupFile that sets JWT_SECRET to a fixed test-only value via
`??=`, so a real .env still wins where one exists. Tests are now hermetic:
clone the repo, `pnpm install`, `pnpm --filter server test` → 477/477 pass.
