feat(frontend): add failover API layer and TanStack Query hooks

Add frontend data layer for failover management:

- Add failover.ts API: Tauri invoke wrappers for all failover commands
- Add failover.ts query hooks: TanStack Query mutations and queries
  - useProxyTargets, useProviderHealth queries
  - useSetProxyTarget, useResetCircuitBreaker mutations
  - useCircuitBreakerConfig query and mutation
- Update queries.ts with provider health query key
- Update mutations.ts to invalidate health on provider changes
- Add CircuitBreakerConfig and ProviderHealth types

src/lib/api/failover.ts

@@ -0,0 +1,73 @@
+import { invoke } from "@tauri-apps/api/core";
+import type {
+  ProviderHealth,
+  CircuitBreakerConfig,
+  CircuitBreakerStats,
+} from "@/types/proxy";
+
+export interface Provider {
+  id: string;
+  name: string;
+  settingsConfig: unknown;
+  websiteUrl?: string;
+  category?: string;
+  createdAt?: number;
+  sortIndex?: number;
+  notes?: string;
+  meta?: unknown;
+  icon?: string;
+  iconColor?: string;
+  isProxyTarget?: boolean;
+}
+
+export const failoverApi = {
+  // 获取代理目标列表
+  async getProxyTargets(appType: string): Promise<Provider[]> {
+    return invoke("get_proxy_targets", { appType });
+  },
+
+  // 设置代理目标
+  async setProxyTarget(
+    providerId: string,
+    appType: string,
+    enabled: boolean,
+  ): Promise<void> {
+    return invoke("set_proxy_target", { providerId, appType, enabled });
+  },
+
+  // 获取供应商健康状态
+  async getProviderHealth(
+    providerId: string,
+    appType: string,
+  ): Promise<ProviderHealth> {
+    return invoke("get_provider_health", { providerId, appType });
+  },
+
+  // 重置熔断器
+  async resetCircuitBreaker(
+    providerId: string,
+    appType: string,
+  ): Promise<void> {
+    return invoke("reset_circuit_breaker", { providerId, appType });
+  },
+
+  // 获取熔断器配置
+  async getCircuitBreakerConfig(): Promise<CircuitBreakerConfig> {
+    return invoke("get_circuit_breaker_config");
+  },
+
+  // 更新熔断器配置
+  async updateCircuitBreakerConfig(
+    config: CircuitBreakerConfig,
+  ): Promise<void> {
+    return invoke("update_circuit_breaker_config", { config });
+  },
+
+  // 获取熔断器统计信息
+  async getCircuitBreakerStats(
+    providerId: string,
+    appType: string,
+  ): Promise<CircuitBreakerStats | null> {
+    return invoke("get_circuit_breaker_stats", { providerId, appType });
+  },
+};