JVNAUTOSCI-1679 Replace lexical paper ranking with semantic materialisation

[witbrock]

Summary

• replace the English-coupled lexical ranking core with a semantic materialisation service
• store generic subject-paper recommendation assertions and workflow/prompt support in Vontology-facing services
• trigger bounded recommendation refreshes from profile updates, paper materialisation, and event-driven workflow paths

Validation

• pdm run pyright src/backend/services/paper_recommendation_constants.py src/backend/services/paper_recommendation_materialisation_service.py src/backend/services/paper_recommendation_profile_vontology_service.py src/backend/services/paper_recommendation_ranking_service.py src/backend/services/paper_recommendation_review_service.py src/backend/services/paper_recommendation_vontology_service.py src/backend/services/paper_recommendation_workflow_vontology_service.py src/backend/services/arxiv_paper_link_service.py src/backend/server/routes/settings_routes.py src/backend/server/utils_flask.py src/backend/services/__init__.py
• pdm run pytest tests/backend/test_paper_recommendation_profile_vontology_service.py tests/backend/test_paper_recommendation_review_service.py tests/backend/test_paper_recommendation_ranking_service.py tests/backend/test_paper_recommendation_materialisation_service.py tests/backend/test_recommendation_profile_routes.py tests/backend/test_internal_mcp_paper_recommendations_gateway.py tests/backend/test_mcp_stdio_server_exposes_paper_recommendations.py tests/backend/test_utils_flask_orchestrator_startup.py tests/backend/test_utils_flask_identity_resolution_bootstrap.py tests/backend/test_arxiv_paper_link_service.py tests/backend/test_internal_mcp_catalogue_builds.py tests/backend/test_internal_mcp_error_responses.py tests/backend/test_internal_mcp_dynamic_tool_registration.py -q