feat(acceptance): 增加生产同构媒体压力验收模式

引入动态流量门禁、隔离验收身份与协议级 Gemini/Volces 模拟器，覆盖双站点 API、Worker、PostgreSQL、River、账务、回调和媒体物化链路。

新增 P24/P28/P32 容量阶梯、Worker 强杀恢复、真实小流量 canary、CAS 放量和失败保持 validation 的生产编排；Worker 执行槽、连接池、媒体并发和双站点副本数改为环境配置。

验证：Go 全量测试、真实 PostgreSQL 迁移集成测试、迁移安全检查、OpenAPI 生成、ShellCheck、Kustomize、gofmt 和 git diff --check。

apps/api/internal/httpapi/volces_compat_handlers_test.go

@@ -1,6 +1,9 @@
 package httpapi
 
 import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"
 
@@ -35,3 +38,25 @@ func TestVolcesCompatibleTaskBuildsProtocolResponseFromCanonicalResult(t *testin
 		}
 	}
 }
+
+func TestVolcesCompatibilityPreservesValidationGateStatus(t *testing.T) {
+	recorder := httptest.NewRecorder()
+	writeVolcesCompatibleTaskError(recorder, &gatewayTaskCreationError{
+		Stage: gatewayTaskCreationPrepare,
+		Err: &taskTrafficError{
+			Status:  http.StatusServiceUnavailable,
+			Code:    "validation_in_progress",
+			Message: "new production tasks are paused while validation is running",
+		},
+	})
+	if recorder.Code != http.StatusServiceUnavailable {
+		t.Fatalf("status=%d body=%s", recorder.Code, recorder.Body.String())
+	}
+	var payload VolcesErrorEnvelope
+	if err := json.NewDecoder(recorder.Body).Decode(&payload); err != nil {
+		t.Fatalf("decode error: %v", err)
+	}
+	if payload.Error.Code != "validation_in_progress" {
+		t.Fatalf("error=%+v", payload.Error)
+	}
+}