feat(worker): 实现集群限流与自适应负载

保留平台模型 RPM、TPM 和并发策略语义，增加 PostgreSQL 集群级租约、饱和候选重选和多平台自动负载，避免突发任务固定等待首个平台。\n\n新增 Worker 实时负载采样、自适应 active/heavy 容量、心跳与管理端指标，并扩展本地 acceptance runner，覆盖三 Worker、同模型三平台 2/4/6 并发和 48 个带图视频突发任务。\n\n验证：go test ./...、go vet ./...、PostgreSQL 跨 Store 集成测试、gofmt、bash -n、ShellCheck 及本地集群 provider-burst 验收通过；48/48 成功，无越限、重复提交、重复计费、重复回调或终态资源泄漏。

packages/contracts/src/index.ts

@@ -961,6 +961,43 @@ export interface ModelRateLimitStatus {
   recentPriorityDemotions?: PriorityDemotionRecord[];
 }
 
+export interface WorkerInstanceRuntime {
+  instanceId: string;
+  podUid?: string;
+  podName?: string;
+  site?: string;
+  revision?: string;
+  status: string;
+  allocatedCapacity: number;
+  capacityLimit: number;
+  hardCapacityLimit: number;
+  safeCapacity: number;
+  heavyCapacity: number;
+  reportedActiveTasks: number;
+  preparingTasks: number;
+  waitingUpstreamTasks: number;
+  finalizingTasks: number;
+  pressureState: 'normal' | 'busy' | 'critical' | 'unknown' | string;
+  pressureReason?: string;
+  loadSampledAt?: string;
+  runningTasks: number;
+  activeLeases: number;
+  heartbeatAt: string;
+  drainingAt?: string;
+}
+
+export interface WorkerQueueRuntime {
+  queued: number;
+  running: number;
+  oldestWaitSeconds: number;
+}
+
+export interface WorkerClusterRuntime {
+  workers: WorkerInstanceRuntime[];
+  queue: WorkerQueueRuntime;
+  capturedAt: string;
+}
+
 export interface GatewayNetworkProxyConfig {
   globalHttpProxy?: string;
   globalHttpProxySet: boolean;