feat(proxy): implement independent failover queue management

Add a new failover queue system that operates independently from provider
sortIndex, allowing users to configure failover order per app type.

Backend changes:
- Add failover_queue table to schema.rs for persistent storage
- Create dao/failover.rs with CRUD operations for queue management
- Add Tauri commands for queue operations (get, add, remove, reorder, toggle)
- Refactor provider_router.rs select_providers() to use failover queue:
  - Current provider always takes first priority
  - Queue providers ordered by queue_order as fallback
  - Only providers with open circuit breakers are included

Frontend changes:
- Add FailoverQueueItem type to proxy.ts
- Extend failover.ts API with queue management methods
- Add React Query hooks for queue data fetching and mutations
- Create FailoverQueueManager component with drag-and-drop reordering
- Integrate queue management into SettingsPage under "Auto Failover"
- Add i18n translations for zh and en locales

src/lib/api/failover.ts

@@ -3,6 +3,7 @@ import type {
   ProviderHealth,
   CircuitBreakerConfig,
   CircuitBreakerStats,
+  FailoverQueueItem,
 } from "@/types/proxy";
 
 export interface Provider {
@@ -21,6 +22,8 @@ export interface Provider {
 }
 
 export const failoverApi = {
+  // ========== 旧版代理目标 API（保留向后兼容）==========
+
   // 获取代理目标列表
   async getProxyTargets(appType: string): Promise<Provider[]> {
     return invoke("get_proxy_targets", { appType });
@@ -35,6 +38,8 @@ export const failoverApi = {
     return invoke("set_proxy_target", { providerId, appType, enabled });
   },
 
+  // ========== 熔断器 API ==========
+
   // 获取供应商健康状态
   async getProviderHealth(
     providerId: string,
@@ -70,4 +75,49 @@ export const failoverApi = {
   ): Promise<CircuitBreakerStats | null> {
     return invoke("get_circuit_breaker_stats", { providerId, appType });
   },
+
+  // ========== 故障转移队列 API（新） ==========
+
+  // 获取故障转移队列
+  async getFailoverQueue(appType: string): Promise<FailoverQueueItem[]> {
+    return invoke("get_failover_queue", { appType });
+  },
+
+  // 获取可添加到队列的供应商（不在队列中的）
+  async getAvailableProvidersForFailover(appType: string): Promise<Provider[]> {
+    return invoke("get_available_providers_for_failover", { appType });
+  },
+
+  // 添加供应商到故障转移队列
+  async addToFailoverQueue(
+    appType: string,
+    providerId: string,
+  ): Promise<void> {
+    return invoke("add_to_failover_queue", { appType, providerId });
+  },
+
+  // 从故障转移队列移除供应商
+  async removeFromFailoverQueue(
+    appType: string,
+    providerId: string,
+  ): Promise<void> {
+    return invoke("remove_from_failover_queue", { appType, providerId });
+  },
+
+  // 重新排序故障转移队列
+  async reorderFailoverQueue(
+    appType: string,
+    providerIds: string[],
+  ): Promise<void> {
+    return invoke("reorder_failover_queue", { appType, providerIds });
+  },
+
+  // 设置故障转移队列项的启用状态
+  async setFailoverItemEnabled(
+    appType: string,
+    providerId: string,
+    enabled: boolean,
+  ): Promise<void> {
+    return invoke("set_failover_item_enabled", { appType, providerId, enabled });
+  },
 };