Include tests in TypeScript type-checking
Fix issue where test files were excluded from TypeScript compilation,
causing VS Code to catch type errors that npm run typecheck missed.
Changes:
- Add "tests/**/*" to include array in tsconfig.json
- Remove "tests/**/*" from exclude array
- Tests are now type-checked by both build and typecheck scripts
- Tests are emitted to dist/tests/ (harmless locally, can exclude from npm publish later)
This ensures type errors in tests are caught by:
- npm run typecheck (local development)
- npm run build (before commits)
- CI pipeline (prevents broken tests from being merged)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>