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/cmd/acceptance-emulator/main.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"log/slog"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/easyai/easyai-ai-gateway/apps/api/internal/acceptanceemulator"
+)
+
+func main() {
+	address := strings.TrimSpace(os.Getenv("HTTP_ADDR"))
+	if address == "" {
+		address = ":8090"
+	}
+	server := &http.Server{
+		Addr:              address,
+		Handler:           acceptanceemulator.New(acceptanceemulator.Config{}).Handler(),
+		ReadHeaderTimeout: 10 * time.Second,
+	}
+	slog.Info("acceptance protocol emulator started", "address", address)
+	if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+		slog.Error("acceptance protocol emulator stopped", "error", err)
+		os.Exit(1)
+	}
+}