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

tests/components/ProviderList.test.tsx

@@ -125,7 +125,6 @@ describe("ProviderList Component", () => {
         onDelete={vi.fn()}
         onDuplicate={vi.fn()}
         onOpenWebsite={vi.fn()}
-        onSetProxyTarget={vi.fn()}
         isLoading
       />,
     );
@@ -154,7 +153,6 @@ describe("ProviderList Component", () => {
         onDelete={vi.fn()}
         onDuplicate={vi.fn()}
         onOpenWebsite={vi.fn()}
-        onSetProxyTarget={vi.fn()}
         onCreate={handleCreate}
       />,
     );
@@ -195,7 +193,6 @@ describe("ProviderList Component", () => {
         onDuplicate={handleDuplicate}
         onConfigureUsage={handleUsage}
         onOpenWebsite={handleOpenWebsite}
-        onSetProxyTarget={vi.fn()}
       />,
     );