Refactor union resolution to explicitly try reference members before
non-reference members. This replaces the previous error-message-based
fallback with a deterministic, structural approach.
- Update `parseValueWithReferences` and `resolveNestedReferences` to
partition members by reference presence.
- Update documentation in `README.md`, `AGENTS.md`, and
`syntax-rework-plan.md` to reflect this behavior.
Implements Phase 1 and 2 of the syntax rework plan:
- Brackets `[]` are now mandatory for all tuple and array values.
- Removed the `[Type][]` array syntax; arrays now only use `Type[]`.
- `[single]` is now strictly a 1-tuple rather than an array.
- Updated documentation and test fixtures to reflect these breaking
changes.