feat(knowledge): 会话级去重 + 知识域地图注入 Planner 解决 ISS-001 重复检索

- RetrievedDocTracker: sessionId → Set<filePath> 会话级去重，LookupKnowledgeTool Step 5 过滤已检索文档
- KnowledgeDomainService: 域级聚合，LLM 生成 when_to_retrieve，构建 knowledge map YAML
- DocumentFieldEnricher: 上传时 LLM 补全 covers + whenToRetrieve（含同域文档排除上下文）
- KnowledgeDomain entity + V009 迁移: 域级元数据持久化，避免重启重复 LLM 调用
- ChatService: 注入 knowledge map 到 Planner prompt，会话结束时清理去重状态
- KnowledgeIndexService: 手写 JSON 解析替换为 Jackson ObjectMapper，启动时补建缺失域记录
- chat-planner-prompt: 新增知识库检索规则（按域 when_to_retrieve 判断，每域最多一次检索）
- doc-field-enricher-prompt / domain-summary-prompt: 外部化 LLM 提示词

src/main/java/com/superbiz/agent/domain/entity/KnowledgeDomain.java

@@ -0,0 +1,51 @@
+package com.superbiz.agent.domain.entity;
+
+import jakarta.persistence.*;
+import lombok.AllArgsConstructor;
+import lombok.Builder;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import java.time.LocalDateTime;
+
+@Entity
+@Table(name = "knowledge_domain")
+@Data
+@Builder
+@NoArgsConstructor
+@AllArgsConstructor
+public class KnowledgeDomain {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(name = "domain_id", unique = true, nullable = false, length = 64)
+    private String domainId;
+
+    @Column(name = "description", length = 256)
+    private String description;
+
+    @Column(name = "when_to_retrieve", columnDefinition = "TEXT")
+    private String whenToRetrieve;
+
+    @Column(name = "document_count", nullable = false)
+    private int documentCount;
+
+    @Column(name = "created_at", nullable = false, updatable = false)
+    private LocalDateTime createdAt;
+
+    @Column(name = "updated_at", nullable = false)
+    private LocalDateTime updatedAt;
+
+    @PrePersist
+    protected void onCreate() {
+        createdAt = LocalDateTime.now();
+        updatedAt = LocalDateTime.now();
+    }
+
+    @PreUpdate
+    protected void onUpdate() {
+        updatedAt = LocalDateTime.now();
+    }
+}