#922 Remove Ollama-only features: generate-workflow, dsl/ask, dsl/search, RAG tools, ragit, SearXNG, ollama service

EARS SPEC: - The API shall not expose /generate-workflow, /dsl/ask or /dsl/search. - The engine shall not register tools.rag.*; tools.search.web shall remain using a non-SearXNG provider. - docker-compose shall not define ollama or searxng services. Parent epic: #913. Synthesis (technical problems / solution domains / alternatives) recorded as a comment when started.