Lift the hardcoded 'nomic-embed-text:v1.5' string out of both
RagService and OllamaService into a shared EMBEDDING_MODEL_NAME
constant in constants/ollama.ts. The duplicate in OllamaService
existed only to dodge a circular import with RagService; the
constants module has no service imports, so a shared constant
eliminates both the duplication and the drift risk called out
in the inline "keep in sync" comment.
jakeaturner