perf(gateway): 优化热点路径并补齐高覆盖测试

backend/internal/config/config_test.go

@@ -1010,6 +1010,16 @@ func TestValidateConfigErrors(t *testing.T) {
 			mutate:  func(c *Config) { c.Gateway.UsageRecord.AutoScaleCheckIntervalSeconds = 0 },
 			wantErr: "gateway.usage_record.auto_scale_check_interval_seconds",
 		},
+		{
+			name:    "gateway user group rate cache ttl",
+			mutate:  func(c *Config) { c.Gateway.UserGroupRateCacheTTLSeconds = 0 },
+			wantErr: "gateway.user_group_rate_cache_ttl_seconds",
+		},
+		{
+			name:    "gateway models list cache ttl range",
+			mutate:  func(c *Config) { c.Gateway.ModelsListCacheTTLSeconds = 31 },
+			wantErr: "gateway.models_list_cache_ttl_seconds",
+		},
 		{
 			name:    "gateway scheduling sticky waiting",
 			mutate:  func(c *Config) { c.Gateway.Scheduling.StickySessionMaxWaiting = 0 },