Self-describing meta-schemas: add @context giving RDF semantics to the keywords (oold-meta -> WoT JSON-Schema-in-RDF; oold-ui -> SHACL 1.2 UI) #82

Idea

Make the OO-LD meta-schemas themselves OO-LD documents by giving them an @context that assigns RDF semantics to the schema keywords they define. This dogfoods the core thesis ("the artefact is the source") one level up: the vocabulary that describes OO-LD schemas becomes machine-readable about what each keyword means, not just how it is shaped.

Proposal

meta/oold-meta-schema.json - add an @context mapping the JSON Schema keywords to the W3C WoT "JSON Schema in RDF" vocabulary (namespace https://www.w3.org/2019/wot/json-schema#), and the x-oold-* keywords to the OO-LD vocabulary namespace already declared via $vocabulary. WoT provides stable IRIs for JSON Schema constructs: properties, propertyName, enum, const, required, minimum, maximum, exclusiveMinimum/exclusiveMaximum, and the type kinds as classes (ObjectSchema, StringSchema, IntegerSchema, ArraySchema, DataSchema).

meta/oold-ui-meta-schema.json - add an @context mapping the x-oold-ui-* keywords to SHACL 1.2 UI terms:

Why

• The meta-schema becomes self-describing: an RDF tool can learn that OO-LD's properties is WoT jsonschema:properties, that x-oold-ui-property-order is sh:order, etc.
• It is the machine-readable backing for the SHACL/OWL generation crosswalk in Align x-oold-range / x-oold-ui-* with SHACL 1.2 (Core, Node Expressions, User Interfaces) #76 (this issue supplies the term identities; Align x-oold-range / x-oold-ui-* with SHACL 1.2 (Core, Node Expressions, User Interfaces) #76 uses them to emit shapes).
• Pure win for compatibility: the @context is ignored by JSON Schema validators and makes each meta-schema a valid JSON-LD remote context, exactly like any other OO-LD document.

Caveats

• The WoT mapping is partial/approximate: JSON Schema type: string corresponds to the WoT StringSchema class rather than a type property, so the @context covers the property-like keywords cleanly and the type kinds need a coercion or are documented as class-valued.
• SHACL 1.2 UI is a First Public Working Draft (2026); shui: terms may change - pin a dated version and revisit.

Scope

• Add the two @context blocks; verify each meta-schema still validates as plain JSON Schema 2020-12 and expands as a JSON-LD context.
• A small test that the meta-schema @context expands without error (jsonld.js).

Related: #76 (SHACL crosswalk / generation), #77 (delivery). Not covered by the closed #6/#41 (which added the meta-schema and $vocabulary, not keyword RDF semantics).