feat(rag): modularize knowledge retrieval pipeline

src/main/java/com/superbiz/agent/dto/RerankTrace.java

@@ -0,0 +1,26 @@
+package com.superbiz.agent.dto;
+
+import lombok.Builder;
+import lombok.Data;
+
+import java.util.List;
+
+/**
+ * Rule-based rerank explanation for final evidence blocks.
+ */
+@Data
+@Builder
+public class RerankTrace {
+
+    private List<Item> items;
+
+    @Data
+    @Builder
+    public static class Item {
+        private Integer finalRank;
+        private String source;
+        private Double baseScore;
+        private Double finalScore;
+        private List<String> boostReasons;
+    }
+}