Merge branch 'refactor/backend-architecture' into development

api/app/features/memory/retriever.py

@@ -0,0 +1,8 @@
+"""Hybrid retriever — metadata filter + FTS + vector retrieval + score fusion (skeleton)."""
+
+
+class HybridRetriever:
+    """Phase 2+ implementation: combine FTS, vector, and metadata filter results."""
+
+    async def retrieve(self, user_id: str, query: str, *, top_k: int = 10) -> list[dict]:
+        raise NotImplementedError