Surface the instance-side object-graph runtime as a headline feature (docs + example)

[simontaurus]

Context

The review of the polyglot-modeling landscape (w3c/yaml-ld#19: LinkML, SPDX 3.0, jargon.sh, TreeLDR, Croissant, OCA, REST-API-LD) found that OO-LD's most novel and least-marketed capability is its instance-side object-graph runtime: OO-LD instances are simultaneously valid JSON-LD documents, and oold-python resolves IRIs into lazily-loaded object references. The compile-based peers mostly stop at emitting a context; they do not define dual-consumable instances or a resolution runtime.

Scope

• A headline docs page + runnable example showing lazy IRI -> object resolution (link/load a referenced object on attribute access), building on the existing linked_data_editor example.
• Cross-link from the spec intro's sharpened positioning (see spec PR).

Acceptance

• Example notebook/script demonstrating attribute-access resolution of a referenced object across two schemas.