feat(phase1): 完成文档查询和删除接口

Task 5.4: 文档查询接口
- DocumentManagementService 新增查询方法：
  - queryDocumentById: 根据 docId 查询单个文档
  - queryDocumentsByStatus: 根据状态查询（分页）
  - queryDocumentsByFaultSource: 根据故障源查询
  - convertToResponse: 实体转 DTO 工具方法
- DocumentController 新增 RESTful 接口：
  - GET /api/documents/{docId}
  - GET /api/documents/status/{status}?page=0&size=20
  - GET /api/documents/faultSource/{faultSource}

Task 5.5: 文档删除接口
- DocumentManagementService 新增删除方法：
  - deleteDocument: 删除文档元数据
  - TODO: 向量索引删除待实现
- DocumentController 新增删除接口：
  - DELETE /api/documents/{docId}

功能特性：
- 统一异常处理：DocumentProcessException
- 统一响应格式：Result<T>
- 分页支持：Page/PageRequest
- 事务支持：@Transactional

编译验证：BUILD SUCCESS

Progress: 28/33 tasks completed (85%)

src/main/java/com/superbiz/agent/service/DocumentManagementService.java

@@ -3,11 +3,14 @@ package com.superbiz.agent.service;
 import com.superbiz.agent.domain.entity.ApiDocument;
 import com.superbiz.agent.domain.enums.FaultCategory;
 import com.superbiz.agent.dto.DocumentChunk;
+import com.superbiz.agent.dto.DocumentQueryResponse;
 import com.superbiz.agent.dto.DocumentUploadRequest;
 import com.superbiz.agent.exception.DocumentProcessException;
 import com.superbiz.agent.repository.ApiDocumentRepository;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.PageRequest;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
 import org.springframework.web.multipart.MultipartFile;
@@ -18,6 +21,7 @@ import java.time.LocalDateTime;
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
+import java.util.stream.Collectors;
 
 /**
  * 文档管理服务
@@ -158,4 +162,76 @@ public class DocumentManagementService {
             return FaultCategory.EXTERNAL_API;
         }
     }
+
+    /**
+     * 根据 docId 查询文档
+     */
+    public DocumentQueryResponse queryDocumentById(String docId) {
+        Optional<ApiDocument> optional = apiDocumentRepository.findByDocId(docId);
+        if (optional.isEmpty()) {
+            throw new DocumentProcessException(docId, "query", "文档不存在");
+        }
+
+        ApiDocument doc = optional.get();
+        return convertToResponse(doc);
+    }
+
+    /**
+     * 根据状态查询文档列表（分页）
+     */
+    public List<DocumentQueryResponse> queryDocumentsByStatus(String status, int page, int size) {
+        Page<ApiDocument> documents = apiDocumentRepository.findByStatus(status, PageRequest.of(page, size));
+        return documents.stream()
+            .map(this::convertToResponse)
+            .collect(Collectors.toList());
+    }
+
+    /**
+     * 根据故障源查询文档列表
+     */
+    public List<DocumentQueryResponse> queryDocumentsByFaultSource(String faultSource) {
+        List<ApiDocument> documents = apiDocumentRepository.findByFaultSource(faultSource);
+        return documents.stream()
+            .map(this::convertToResponse)
+            .collect(Collectors.toList());
+    }
+
+    /**
+     * 删除文档
+     */
+    @Transactional
+    public void deleteDocument(String docId) {
+        Optional<ApiDocument> optional = apiDocumentRepository.findByDocId(docId);
+        if (optional.isEmpty()) {
+            throw new DocumentProcessException(docId, "delete", "文档不存在");
+        }
+
+        ApiDocument doc = optional.get();
+
+        // TODO: 删除向量索引
+        log.warn("向量索引删除功能待实现，docId: {}", docId);
+
+        // 删除元数据
+        apiDocumentRepository.delete(doc);
+        log.info("文档已删除，docId: {}", docId);
+    }
+
+    /**
+     * 转换为响应 DTO
+     */
+    private DocumentQueryResponse convertToResponse(ApiDocument doc) {
+        return DocumentQueryResponse.builder()
+            .docId(doc.getDocId())
+            .fileName(doc.getFileName())
+            .faultCategory(doc.getFaultCategory().name())
+            .faultSource(doc.getFaultSource())
+            .apiName(doc.getApiName())
+            .version(doc.getVersion())
+            .fileSize(doc.getFileSize())
+            .status(doc.getStatus())
+            .chunkCount(doc.getChunkCount())
+            .indexedAt(doc.getIndexedAt())
+            .createdAt(doc.getCreatedAt())
+            .build();
+    }
 }