Merge branch 'refactor/backend-architecture' into development

api/app/ports/reranker.py

@@ -0,0 +1,10 @@
+"""Reranker port — 可选，二期 cross-encoder rerank 能力契约。"""
+
+from typing import Protocol, runtime_checkable
+
+
+@runtime_checkable
+class Reranker(Protocol):
+    async def rerank(self, query: str, documents: list[str]) -> list[float]:
+        """Score documents against a query, return relevance scores."""
+        ...