feat(knowledge): 添加知识库标签统计功能

- 在 KnowledgeItemApplicationService 中注入 TagMapper 并调用统计方法
- 新增 countKnowledgeSetTags 方法用于计算知识库中的标签总数
- 在 KnowledgeManagementStatisticsResponse 中添加 totalTags 字段
- 在前端 KnowledgeManagementPage 中显示标签总数统计信息
- 更新统计卡片布局从 3 列改为 4 列以适应新增统计项
- 在知识管理模型中添加 totalTags 类型定义

backend/services/data-management-service/src/main/java/com/datamate/datamanagement/application/KnowledgeItemApplicationService.java

@@ -16,6 +16,7 @@ import com.datamate.datamanagement.domain.model.knowledge.KnowledgeItem;
 import com.datamate.datamanagement.domain.model.knowledge.KnowledgeSet;
 import com.datamate.datamanagement.infrastructure.config.DataManagementProperties;
 import com.datamate.datamanagement.infrastructure.exception.DataManagementErrorCode;
+import com.datamate.datamanagement.infrastructure.persistence.mapper.TagMapper;
 import com.datamate.datamanagement.infrastructure.persistence.repository.DatasetFileRepository;
 import com.datamate.datamanagement.infrastructure.persistence.repository.DatasetRepository;
 import com.datamate.datamanagement.infrastructure.persistence.repository.KnowledgeItemRepository;
@@ -86,6 +87,7 @@ public class KnowledgeItemApplicationService {
     private final DatasetRepository datasetRepository;
     private final DatasetFileRepository datasetFileRepository;
     private final DataManagementProperties dataManagementProperties;
+    private final TagMapper tagMapper;
 
     public KnowledgeItem createKnowledgeItem(String setId, CreateKnowledgeItemRequest request) {
         KnowledgeSet knowledgeSet = requireKnowledgeSet(setId);
@@ -233,6 +235,7 @@ public class KnowledgeItemApplicationService {
         long datasetFileSize = safeLong(knowledgeItemRepository.sumDatasetFileSize());
         long uploadFileSize = calculateUploadFileTotalSize();
         response.setTotalSize(datasetFileSize + uploadFileSize);
+        response.setTotalTags(safeLong(tagMapper.countKnowledgeSetTags()));
 
         return response;
     }

backend/services/data-management-service/src/main/java/com/datamate/datamanagement/infrastructure/persistence/mapper/TagMapper.java

@@ -14,6 +14,7 @@ public interface TagMapper {
     List<Tag> findByIdIn(@Param("ids") List<String> ids);
     List<Tag> findByKeyword(@Param("keyword") String keyword);
     List<Tag> findAllByOrderByUsageCountDesc();
+    Long countKnowledgeSetTags();
 
     int insert(Tag tag);
     int update(Tag tag);

backend/services/data-management-service/src/main/java/com/datamate/datamanagement/interfaces/dto/KnowledgeManagementStatisticsResponse.java

@@ -12,4 +12,5 @@ public class KnowledgeManagementStatisticsResponse {
     private Long totalKnowledgeSets = 0L;
     private Long totalFiles = 0L;
     private Long totalSize = 0L;
+    private Long totalTags = 0L;
 }

backend/services/data-management-service/src/main/resources/mappers/TagMapper.xml

@@ -53,6 +53,19 @@
         ORDER BY usage_count DESC, name ASC
     </select>
 
+    <select id="countKnowledgeSetTags" resultType="long">
+        SELECT COUNT(DISTINCT t.id)
+        FROM t_dm_tags t
+        WHERE EXISTS (
+            SELECT 1
+            FROM t_dm_knowledge_sets ks
+            WHERE ks.tags IS NOT NULL
+              AND JSON_VALID(ks.tags) = 1
+              AND JSON_LENGTH(ks.tags) > 0
+              AND JSON_SEARCH(ks.tags, 'one', t.name, NULL, '$[*].name') IS NOT NULL
+        )
+    </select>
+
     <insert id="insert" parameterType="com.datamate.datamanagement.domain.model.dataset.Tag">
         INSERT INTO t_dm_tags (id, name, description, category, color, usage_count)
         VALUES (#{id}, #{name}, #{description}, #{category}, #{color}, #{usageCount})