The build step runs `tsc && vite build`, and the test files that import
Node.js built-ins (fs, path) and use __dirname were causing TS2307 and
TS2304 errors during compilation. Excluding test files from tsconfig
keeps the build clean while vitest handles its own TypeScript resolution.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>