feat(rag): chunk evidence identity, dedup, and search port

Preserve same-document multi-chunk evidence with evidenceKey identity,
per-document caps, retrieve-k/return-n split, and a dense KnowledgeSearchPort.
Archives Delivery 1 OpenSpec change as the foundation for hybrid retrieval.

src/main/java/com/superbiz/agent/service/retrieval/KnowledgeSearchHit.java

@@ -0,0 +1,24 @@
+package com.superbiz.agent.service.retrieval;
+
+import java.util.Map;
+
+/**
+ * Normalized search hit returned by {@link KnowledgeSearchPort}.
+ */
+public record KnowledgeSearchHit(
+        String id,
+        String content,
+        Double score,
+        Double rawScore,
+        String scoreLabel,
+        String metadataJson,
+        Map<String, String> metadata,
+        String docId,
+        Integer chunkIndex,
+        String evidenceKey,
+        String source,
+        String title,
+        String breadcrumb,
+        int originalRank
+) {
+}