feat(search): recherche semantique - embeddings vectoriels + hybride RRF (#70)

backend/services/search.py

@@ -56,11 +56,13 @@ def advanced_search_vaults(
     created: str | None = None,
     modified: str | None = None,
     size: str | None = None,
+    semantic: bool = False,
 ) -> dict[str, Any]:
     """Advanced full-text search (TF-IDF, facets, operators).
 
-    No permission filtering is applied: callers that need it (the tool layer)
-    filter the ``results`` list themselves.
+    When ``semantic`` is True, the TF-IDF ranking is fused with the embedding
+    (semantic) ranking via RRF. No permission filtering is applied: callers
+    that need it (the tool layer) filter the ``results`` list themselves.
     """
     from backend.search import advanced_search
 
@@ -79,6 +81,7 @@ def advanced_search_vaults(
         created=created,
         modified=modified,
         size=size,
+        semantic=semantic,
     )