MOLE v2.0.0: Octave Readiness

## Objective

Bring the Octave (MATLAB) implementation into compliance with the MOLE 2.0
API, numerical behavior, testing, documentation, and packaging standards.

## Definition of done

- [ ] File organization matches MOLE language specifics
- [ ] Grid structs implemented
- [ ] MOLE operator updates for grid struct are implemented
- [ ] Boundary-condition behavior is consistent with the specification
- [ ] Examples and tutorials are updated
- [ ] Unit and regression tests pass
- [ ] Results agree with the reference implementation
- [ ] Deprecated 1.x interfaces are removed or documented
- [ ] Installation and packaging instructions are current
- [ ] CI tests the supported compiler/interpreter versions
- [ ] Language-specific documentation is complete

## Related work

Individual implementation tasks should be created as sub-issues
and linked below.

**Keep-open request**
- [x] I am requesting maintainer review for `keep-open`.