feat: 集成 AI-Core gRPC 文档解析服务

- 新增 AICoreClient 客户端
- 添加 document_parser_client.go
- 知识库服务集成 AI-Core 解析
- 配置中添加 ai_core_service_addr

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/cmd/api/main.go

@@ -87,7 +87,7 @@ func main() {
 	if err != nil {
 		log.Printf("Warning: Failed to initialize upload service: %v (files will not be available)", err)
 	}
-	knowledgeService := service.NewKnowledgeService(knowledgeRepo, modelRepo, uploadService, cfg.PythonServiceURL)
+	knowledgeService := service.NewKnowledgeService(knowledgeRepo, modelRepo, uploadService, cfg.PythonServiceURL, cfg.AICoreServiceAddr)
 
 	// 6. 初始化 Handler
 	dbHandler := handler.NewDatabaseHandler(dbService)