Add integration tests with actual TypeScript compilation

[bntvllnt]

Problem

Smoke tests only validate JSON structure of tsconfig presets. No test verifies that configs actually compile TypeScript successfully.

Risk

Invalid compiler option combinations could pass JSON validation but fail at compile time.

Acceptance Criteria

• Create minimal .ts files per preset (base, nodejs, node-library, react, nextjs)
• Run tsc --noEmit with each preset config
• Verify clean compilation and expected behavior
• Add to CI pipeline

Priority

Medium — structural tests miss semantic TS errors.