Wire up query history: localStorage session persistence + sidebar UI

apps/ai-service/rag/ports.py

@@ -76,3 +76,12 @@ class SectionRetriever(Protocol):
 
 class ParentStore(Protocol):
     def get(self, parent_id: str) -> ParentDocument | None: ...
+
+
+class SectionListRetriever(Protocol):
+    """The per-drug section checklist Feature-List #4 needs, cheap because
+    `drug_id`/`section_key` are already-indexed Qdrant payload fields — no
+    new indexing. Separate from `SectionRetriever` (interface segregation):
+    this returns labels only, never chunk text."""
+
+    def list_sections(self, drug_id: str) -> list[tuple[str, str]]: ...