feat: target-ontology-adapter §4 Loader pipeline

[deanban]

adapter -> normalizer -> hasher -> materializer loader pipeline: cross-reference resolution, deterministic snapshot hashing, per-facet EnrichmentDecisionRecord derivation, context-card hashing/drift detection, and the LoadedTarget output.

Tracking: #97. Source: openspec/changes/target-ontology-adapter/tasks.md §4.

Tasks

• 4.1 NormalizedTargetModel value object
• 4.2 TargetModelNormalizer.normalize
• 4.3 Dangling property-ref resolution
• 4.4 Dangling vocabulary-ref resolution
• 4.5 Dangling FK-ref resolution
• 4.6 Stable ordering invariants
• 4.7 Reject DTOs carrying snapshot_hash field
• 4.8 SnapshotHasher.hash (SHA-256 hex)
• 4.9 Canonical-JSON serializer
• 4.10 Pinned golden-manifest digest
• 4.11 Facet + EnrichmentStatus enums
• 4.11a FacetDecision model
• 4.11b EnrichmentDecisionRecord (all five facets)
• 4.12 Effective-completeness resolution
• 4.13 Per-facet derivation rules
• 4.13a One record per entity composition
• 4.13b iter_terms NotImplementedError -> EXTERNAL routing
• 4.14 enrichment.skip_facets build-config opt-out
• 4.14a card_hash computation in loader
• 4.14b CardContentDriftError
• 4.14c aggregate_context_card_version derivation
• 4.15 LoadedTarget model
• 4.16 load_target orchestration
• 4.17 Stage-counter spy for ordering invariant
• 4.18 Cross-ref rejection tests
• 4.19 Ordering-invariance tests
• 4.20 Hasher determinism tests
• 4.21 Hasher rejects snapshot_hash test
• 4.22 Pinned-digest CI test
• 4.23 Per-facet derivation table-driven tests
• 4.23a One-record-per-entity test
• 4.23b card_hash determinism + drift tests
• 4.23c aggregate_context_card_version tests
• 4.24 skip_facets opt-out tests
• 4.25 Lazy selected_refs test
• 4.26 LoaderStageOrderError test