docs(type-nuances): add JavaScript type nuances concept page with tests

Add comprehensive documentation covering:
- JavaScript's dynamic typing vs static typing (TypeScript, Rust, Java)
- null vs undefined semantics and when to use each
- Short-circuit evaluation with &&, ||, ??, and ?.
- typeof operator quirks including the typeof null bug
- instanceof and Symbol.hasInstance customization
- Symbols for unique identifiers and well-known symbols
- BigInt for arbitrary precision integers

Includes 85 passing tests covering all code examples.