feat(ui): add auto-failover configuration UI and provider health display

Add comprehensive UI for failover management:

Components:
- ProviderHealthBadge: Display provider health status with color coding
- CircuitBreakerConfigPanel: Configure failure/success thresholds,
  timeout duration, and error rate limits
- AutoFailoverConfigPanel: Manage proxy targets with drag-and-drop
  priority ordering and individual enable/disable controls
- ProxyPanel: Integrate failover tabs for unified proxy management

Provider enhancements:
- ProviderCard: Show health badge and proxy target indicator
- ProviderActions: Add "Set as Proxy Target" action
- EditProviderDialog: Add is_proxy_target toggle
- ProviderList: Support proxy target filtering mode

Other:
- Update App.tsx routing for settings integration
- Update useProviderActions hook with proxy target mutation
- Fix ProviderList tests for updated component API

src/components/settings/SettingsPage.tsx

@@ -20,6 +20,7 @@ import { AboutSection } from "@/components/settings/AboutSection";
 import { ProxyPanel } from "@/components/proxy";
 import { PricingConfigPanel } from "@/components/usage/PricingConfigPanel";
 import { ModelTestConfigPanel } from "@/components/usage/ModelTestConfigPanel";
+import { AutoFailoverConfigPanel } from "@/components/proxy/AutoFailoverConfigPanel";
 import { UsageDashboard } from "@/components/usage/UsageDashboard";
 import { useSettings } from "@/hooks/useSettings";
 import { useImportExport } from "@/hooks/useImportExport";
@@ -222,6 +223,9 @@ export function SettingsPage({
                   {/* 模型测试配置 */}
                   <ModelTestConfigPanel />
 
+                  {/* 自动故障转移配置 */}
+                  <AutoFailoverConfigPanel />
+
                   <ImportExportSection
                     status={importStatus}
                     selectedFile={selectedFile}