chore(rag): add eval knowledge base mirror

knowledge_base/rag-eval/README.md

@@ -0,0 +1,18 @@
+# RAG Eval Knowledge Base Mirror
+
+This folder stores the committed knowledge-base copy of the canonical RAG eval
+documents.
+
+The source of truth for the eval importer remains:
+
+```text
+eval/rag-retrieval/seed-docs/
+```
+
+The documents are kept under `knowledge_base/rag-eval/` so eval/test knowledge
+does not mix with the normal business knowledge folders such as `api`,
+`infrastructure`, or `troubleshooting`.
+
+Each document keeps its original frontmatter `category` and `kb_scope`. The
+category is still the retrieval category used by L0/L1, while `kb_scope:
+rag-eval` isolates these documents during eval runs.