JVNAUTOSCI-1552 Replace metadata classification with pure-instance semantics

[witbrock]

Summary

• replace /entity_counts and /instances runtime classification with shared structural pure-instance semantics
• add additive pure-instance stats fields and retire the runtime metadata.concept_type index path
• absorb the remaining JVNAUTOSCI-364 concept metadata title cleanup by removing the last live import fallback and switching import name resolution to
  ames[]/top-level
  ame

Validation

• pdm run pytest tests/backend/test_structural_canonical_consistency.py -q
• pdm run pytest tests/backend/test_vontology_concept_stats_service.py -q
• pdm run pytest tests/backend/test_vontology_instance_counts_stats_route.py -q
• pdm run pytest tests/backend/test_vontology_entity_instances_routes.py -q
• pdm run pytest tests/backend/test_virtual_code_predicate_concepts.py -q
• pdm run pytest tests/backend/test_preserved_fields_guardrails.py -q
• pdm run pytest tests/backend/test_concept_import_names_guardrails.py -q
• pdm run pytest tests/backend/test_chat_concept_reference_service.py -q
• pdm run pyright src/backend/db/mongo_client.py src/backend/server/routes/vontology_routes.py src/backend/services/concept_normalization.py src/backend/services/concept_service.py src/backend/services/vontology_concept_stats_service.py src/backend/vontology/utils_vontology.py tests/backend/test_concept_import_names_guardrails.py tests/backend/test_structural_canonical_consistency.py tests/backend/test_vontology_concept_stats_service.py tests/backend/test_vontology_entity_instances_routes.py

Jira

• JVNAUTOSCI-1552
• absorbs the remaining live JVNAUTOSCI-364 overlap for concept metadata title cleanup