refactor: 将 OpType 字段从枚举类型改为 string 类型

主要变更：
- Operation.OpType: Type → string
- NewFullOperation 参数: opType Type → opType string
- IsValidOpType 参数: opType Type → opType string
- operationMeta.OpType: *Type → *string
- queryclient.ListRequest.OpType: model.Type → string

优点：
- 更灵活，支持动态扩展操作类型
- 不再受限于预定义的枚举常量
- 简化类型转换逻辑

兼容性：
- Type 常量定义保持不变 (OpTypeCreate, OpTypeUpdate 等)
- 使用时需要 string() 转换: string(model.OpTypeCreate)
- 所有单元测试已更新并通过 (100%)

测试结果：
✅ api/adapter - PASS
✅ api/highclient - PASS
✅ api/logger - PASS
✅ api/model - PASS
✅ api/persistence - PASS
✅ api/queryclient - PASS
✅ internal/* - PASS

api/persistence/cursor_worker.go

@@ -40,7 +40,7 @@ func (r *OperationRecord) ToModel() *model.Operation {
 		RequestBodyHash:  &r.RequestBodyHash,
 		ResponseBodyHash: &r.ResponseBodyHash,
 		OpSource:         model.Source(r.OpSource),
-		OpType:           model.Type(r.OpType),
+		OpType:           r.OpType,
 		DoPrefix:         r.DOPrefix,
 		DoRepository:     r.DORepository,
 		ClientIP:         r.ClientIP,

api/persistence/e2e_integration_test.go

@@ -726,7 +726,7 @@ func createE2ETestOperations(count int) []*model.Operation {
 			OpID:         fmt.Sprintf("e2e-op-%d-%d", timestamp, i),
 			Timestamp:    time.Now(),
 			OpSource:     model.OpSourceDOIP,
-			OpType:       model.OpTypeCreate,
+			OpType:       string(model.OpTypeCreate),
 			DoPrefix:     "e2e-test",
 			DoRepository: "e2e-repo",
 			Doid:         fmt.Sprintf("e2e/test/%d", i),

api/persistence/example_test.go

@@ -57,7 +57,7 @@ func Example_dbOnly() {
 	// 5. 构造 Operation（包含 IP 信息）
 	op, err := model.NewFullOperation(
 		model.OpSourceDOIP,
-		model.OpTypeCreate,
+		string(model.OpTypeCreate),
 		"10.1000",
 		"my-repo",
 		"10.1000/my-repo/doc001",
@@ -139,7 +139,7 @@ func Example_dbAndTrustlog() {
 	// 5. 构造 Operation
 	op, err := model.NewFullOperation(
 		model.OpSourceDOIP,
-		model.OpTypeCreate,
+		string(model.OpTypeCreate),
 		"10.1000",
 		"my-repo",
 		"10.1000/my-repo/doc002",
@@ -212,7 +212,7 @@ func Example_trustlogOnly() {
 	// 5. 构造 Operation
 	op, err := model.NewFullOperation(
 		model.OpSourceDOIP,
-		model.OpTypeCreate,
+		string(model.OpTypeCreate),
 		"10.1000",
 		"my-repo",
 		"10.1000/my-repo/doc003",
@@ -278,7 +278,7 @@ func Example_mysqlDatabase() {
 	// 5. 构造并发布 Operation
 	op, err := model.NewFullOperation(
 		model.OpSourceDOIP,
-		model.OpTypeCreate,
+		string(model.OpTypeCreate),
 		"10.1000",
 		"my-repo",
 		"10.1000/my-repo/doc004",
@@ -349,7 +349,7 @@ func Example_sqliteDatabase() {
 	// 5. 构造并发布 Operation
 	op, err := model.NewFullOperation(
 		model.OpSourceDOIP,
-		model.OpTypeCreate,
+		string(model.OpTypeCreate),
 		"10.1000",
 		"my-repo",
 		"10.1000/my-repo/doc005",

api/persistence/repository_test.go

@@ -44,7 +44,7 @@ func setupTestDB(t *testing.T) *sql.DB {
 func createTestOperation(t *testing.T, opID string) *model.Operation {
 	op, err := model.NewFullOperation(
 		model.OpSourceDOIP,
-		model.OpTypeCreate,
+		string(model.OpTypeCreate),
 		"10.1000",
 		"test-repo",
 		"10.1000/test-repo/"+opID,