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/acceptanceworkload/profiles.go

@@ -0,0 +1,52 @@
+package acceptanceworkload
+
+import "time"
+
+type GeminiProfile struct {
+	Name        string
+	Requests    int
+	InputBytes  int
+	OutputBytes int
+	DelayMin    time.Duration
+	DelayMax    time.Duration
+}
+
+var (
+	GeminiBaseline = GeminiProfile{
+		Name: "gemini-baseline", Requests: 1000, InputBytes: 256 << 10, OutputBytes: 256 << 10,
+		DelayMin: 4 * time.Second, DelayMax: 4 * time.Second,
+	}
+	GeminiLarge = GeminiProfile{
+		Name: "gemini-large", Requests: 128, InputBytes: 2 << 20, OutputBytes: 4 << 20,
+		DelayMin: 8 * time.Second, DelayMax: 15 * time.Second,
+	}
+	GeminiPeak = GeminiProfile{
+		Name: "gemini-peak", Requests: 32, InputBytes: 8 << 20, OutputBytes: 8 << 20,
+		DelayMin: 15 * time.Second, DelayMax: 30 * time.Second,
+	}
+)
+
+func GeminiProfileByName(name string) (GeminiProfile, bool) {
+	switch name {
+	case GeminiBaseline.Name:
+		return GeminiBaseline, true
+	case GeminiLarge.Name:
+		return GeminiLarge, true
+	case GeminiPeak.Name:
+		return GeminiPeak, true
+	default:
+		return GeminiProfile{}, false
+	}
+}
+
+// VideoImageCount provides a deterministic 60/30/10 split for 3/6/9-image tasks.
+func VideoImageCount(index int) int {
+	switch index % 10 {
+	case 0, 1, 2, 3, 4, 5:
+		return 3
+	case 6, 7, 8:
+		return 6
+	default:
+		return 9
+	}
+}