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/securityevents/metrics_test.go

@@ -7,17 +7,24 @@ import (
 	"strings"
 	"testing"
 	"time"
+
+	"github.com/easyai/easyai-ai-gateway/apps/api/internal/store"
 )
 
 type metricsSnapshot struct {
 	mode string
 	last time.Time
+	pool store.PostgresPoolMetricsSnapshot
 }
 
 func (m metricsSnapshot) SecurityEventMetrics(context.Context, string, string) (string, *time.Time, error) {
 	return m.mode, &m.last, nil
 }
 
+func (m metricsSnapshot) PostgresPoolMetrics() store.PostgresPoolMetricsSnapshot {
+	return m.pool
+}
+
 func TestMetricsExposeBoundedOutcomesAndState(t *testing.T) {
 	metrics := &Metrics{}
 	metrics.ObserveReceipt("accepted", 20*time.Millisecond, 2)
@@ -34,7 +41,14 @@ func TestMetricsExposeBoundedOutcomesAndState(t *testing.T) {
 	metrics.ObserveTaskEventSkip("budget_exceeded")
 
 	recorder := httptest.NewRecorder()
-	metrics.Handler(metricsSnapshot{mode: "push_healthy", last: time.Now().Add(-time.Minute)}, "issuer", "audience", true).
+	metrics.Handler(metricsSnapshot{
+		mode: "push_healthy",
+		last: time.Now().Add(-time.Minute),
+		pool: store.PostgresPoolMetricsSnapshot{
+			MaxConnections: 32, TotalConnections: 18, AcquiredConnections: 12,
+			IdleConnections: 6, EmptyAcquireCount: 3, CanceledAcquireCount: 1,
+		},
+	}, "issuer", "audience", true).
 		ServeHTTP(recorder, httptest.NewRequest(http.MethodGet, "/metrics", nil))
 	if recorder.Code != http.StatusOK {
 		t.Fatalf("metrics status=%d", recorder.Code)
@@ -56,6 +70,12 @@ func TestMetricsExposeBoundedOutcomesAndState(t *testing.T) {
 		`easyai_gateway_concurrency_lease_renewals_total{outcome="lost"} 1`,
 		`easyai_gateway_task_events_skipped_total{outcome="duplicate"} 1`,
 		`easyai_gateway_task_events_skipped_total{outcome="budget_exceeded"} 1`,
+		`easyai_gateway_postgres_pool_max_connections 32`,
+		`easyai_gateway_postgres_pool_total_connections 18`,
+		`easyai_gateway_postgres_pool_acquired_connections 12`,
+		`easyai_gateway_postgres_pool_idle_connections 6`,
+		`easyai_gateway_postgres_pool_empty_acquire_total 3`,
+		`easyai_gateway_postgres_pool_canceled_acquire_total 1`,
 	} {
 		if !strings.Contains(recorder.Body.String(), expected) {
 			t.Fatalf("missing metric %q in:\n%s", expected, recorder.Body.String())