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/acceptance_handlers_test.go

@@ -0,0 +1,27 @@
+package httpapi
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/easyai/easyai-ai-gateway/apps/api/internal/config"
+)
+
+func TestAdmittedTaskRunModeReservesAcceptanceAndProductionSimulation(t *testing.T) {
+	server := &Server{cfg: config.Config{AppEnv: "production"}}
+	for _, runMode := range []string{"simulation", "SIMULATION", "acceptance", "acceptance_canary"} {
+		_, err := server.admittedTaskRunMode(taskTrafficAdmission{}, map[string]any{"runMode": runMode})
+		var trafficErr *taskTrafficError
+		if !errors.As(err, &trafficErr) || trafficErr.Status != 403 {
+			t.Fatalf("run mode %q error=%v", runMode, err)
+		}
+	}
+	for _, runMode := range []string{"acceptance", "acceptance_canary"} {
+		got, err := server.admittedTaskRunMode(taskTrafficAdmission{RunMode: runMode}, map[string]any{
+			"runMode": "production",
+		})
+		if err != nil || got != runMode {
+			t.Fatalf("admitted mode=%q got=%q err=%v", runMode, got, err)
+		}
+	}
+}