Introduce identity model and reconcile upstream imports

Assistant: codex
Assistant-Model: gpt-6-astra
Assistant-Session: 01a070b5-4994-7271-bd8b-7c3dbcedec4b

infospace/models/information-space/InfoTechCanonInformationSpaceModel.md

@@ -421,7 +421,6 @@ InformationSpaceEntity
 ├── MetadataEntity
 │   ├── FrontMatter
 │   ├── MetadataRecord
-│   ├── Identifier
 │   ├── Namespace
 │   ├── Label
 │   ├── Alias
@@ -755,7 +754,9 @@ A **MetadataRecord** is structured data describing an artifact, section, chunk,
 
 ## 11.37 Identifier
 
-An **Identifier** is a stable reference string for an artifact or entity.
+Identifier is imported from [ITC-IDENT](../identity/InfoTechCanonIdentityModel.md).
+The following are artifact-specific conventions over that imported concept,
+not a second general definition.
 
 Recommended properties: