test(acceptance): 增加视频容量阶梯场景

新增 30 至 45 秒模拟上游等待的视频容量场景，使单 Worker 自适应控制在每级突发负载中获得连续占满窗口，同时保持提交、轮询、结果处理和回调全链路。\n\n未修改生产 Worker 和厂商限流逻辑。已执行完整 Go 测试、go vet、gofmt、bash -n、ShellCheck 和生产验收脚本测试。

apps/api/internal/acceptanceemulator/server.go

@@ -674,9 +674,24 @@ func videoDelay(body map[string]any, longRun bool) time.Duration {
 	if longRun {
 		return 2*time.Minute + time.Duration(seed%61)*time.Second
 	}
+	if videoPromptContains(body, "acceptance-capacity-ladder") {
+		return 30*time.Second + time.Duration(seed%16)*time.Second
+	}
 	return 5*time.Second + time.Duration(seed%11)*time.Second
 }
 
+func videoPromptContains(body map[string]any, marker string) bool {
+	content, _ := body["content"].([]any)
+	for _, raw := range content {
+		item, _ := raw.(map[string]any)
+		if strings.TrimSpace(stringValue(item["type"])) == "text" &&
+			strings.Contains(strings.ToLower(stringValue(item["text"])), marker) {
+			return true
+		}
+	}
+	return false
+}
+
 func requestOrigin(r *http.Request) string {
 	scheme := strings.TrimSpace(r.Header.Get("X-Forwarded-Proto"))
 	if scheme == "" {