Write ADR for semantic relations

[monkeypants]

Context

test_semantic_relation.py enforces rules about semantic relations — type safety, the @semantic_relation decorator, relation types (IS_A, PROJECTS, IMPLEMENTS, ENABLES, plus SKOS vocabulary). These tests exist and pass, but there is no ADR explaining:

• Why semantic relations exist in the framework
• What vocabulary is canonical (custom vs SKOS)
• When to use which relation type
• How semantic relations connect to the documentation/viewpoint system

Without this rationale, a contributor can see what the rules are but not why they matter or how to apply them correctly in new bounded contexts.

Acceptance criteria

• ADR drafted explaining the role of semantic relations in the architecture
• ADR covers: canonical vocabulary, SKOS integration rationale, relation type guidance
• ADR references test_semantic_relation.py as the enforcement mechanism
• ADR status: Draft (for socialisation), then Accepted

Related

• src/julee/core/doctrine/test_semantic_relation.py
• Tier 2 priority (working enforcement, missing rationale)