Update documentation to reflect Pattern A architecture

Update electronic_states.md to document the new Pattern A architecture:
- Reference fields now point to ElectronicState instances
- Navigation to parent AtomsState via get_parent_entity() helper
- Eliminates circular references while maintaining clean hierarchy

This completes the documentation updates for the Pattern A refactoring.

Author: ndaelman-hu

docs/atoms_state/electronic_states.md

@@ -74,6 +74,6 @@ Projection quantum numbers cannot exist independently of their parent quantum nu
 
 ## Further Information
 
-The complete implementation resides in `atoms_state.py` within the `nomad_simulations.schema_packages` module. Test cases in `test_atoms_state.py` demonstrate construction patterns and validation behavior. Integration with the tight-binding model method appears in `model_method.py`, where the `TB.resolve_orbital_references()` method shows how to extract orbital information from model systems. Property calculations reference electronic states through fields like `orbitals_state_ref` in the band structure schema.
+The complete implementation resides in `atoms_state.py` within the `nomad_simulations.schema_packages` module. Test cases in `test_atoms_state.py` demonstrate construction patterns and validation behavior. Integration with the tight-binding model method appears in `model_method.py`, where the `TB.resolve_orbital_references()` method shows how to extract orbital information from model systems. Property calculations reference electronic states through entity/orbital reference fields (like `entity_ref` or `orbitals_state_ref`) that point to `ElectronicState` instances. To access the parent `AtomsState`, use the `get_parent_entity()` helper method. This Pattern A architecture eliminates circular references while maintaining clean navigation through the hierarchy.
 
 Users encountering issues or seeking clarification should consult the NOMAD forum at matsci.org, open issues on the GitHub repository, or refer to the main NOMAD documentation for broader context on schema design principles and the normalization system.