refactor(proxy): remove is_proxy_target in favor of failover_queue

- Remove `is_proxy_target` field from Provider struct (Rust & TypeScript)
- Remove related DAO methods: get_proxy_target_provider, set_proxy_target
- Remove deprecated Tauri commands: get_proxy_targets, set_proxy_target
- Add `is_available()` method to CircuitBreaker for availability checks
  without consuming HalfOpen probe permits (used in select_providers)
- Keep `allow_request()` for actual request gating with permit tracking
- Update stream_check to use failover_queue instead of is_proxy_target
- Clean up commented-out reset circuit breaker button in ProviderActions
- Remove unused useProxyTargets and useSetProxyTarget hooks

tests/msw/handlers.ts

@@ -236,4 +236,64 @@ export const handlers = [
   http.post(`${TAURI_ENDPOINT}/sync_current_providers_live`, () =>
     success({ success: true }),
   ),
+
+  // Proxy status (for SettingsPage / ProxyPanel hooks)
+  http.post(`${TAURI_ENDPOINT}/get_proxy_status`, () =>
+    success({
+      running: false,
+      address: "127.0.0.1",
+      port: 0,
+      active_connections: 0,
+      total_requests: 0,
+      success_requests: 0,
+      failed_requests: 0,
+      success_rate: 0,
+      uptime_seconds: 0,
+      current_provider: null,
+      current_provider_id: null,
+      last_request_at: null,
+      last_error: null,
+      failover_count: 0,
+      active_targets: [],
+    }),
+  ),
+
+  http.post(`${TAURI_ENDPOINT}/is_live_takeover_active`, () => success(false)),
+
+  // Failover / circuit breaker defaults
+  http.post(`${TAURI_ENDPOINT}/get_failover_queue`, () => success([])),
+  http.post(`${TAURI_ENDPOINT}/get_available_providers_for_failover`, () =>
+    success([]),
+  ),
+  http.post(`${TAURI_ENDPOINT}/add_to_failover_queue`, () => success(true)),
+  http.post(`${TAURI_ENDPOINT}/remove_from_failover_queue`, () => success(true)),
+  http.post(`${TAURI_ENDPOINT}/reorder_failover_queue`, () => success(true)),
+  http.post(`${TAURI_ENDPOINT}/set_failover_item_enabled`, () => success(true)),
+
+  http.post(`${TAURI_ENDPOINT}/get_circuit_breaker_config`, () =>
+    success({
+      failureThreshold: 3,
+      successThreshold: 2,
+      timeoutSeconds: 60,
+      errorRateThreshold: 50,
+      minRequests: 5,
+    }),
+  ),
+  http.post(`${TAURI_ENDPOINT}/update_circuit_breaker_config`, () =>
+    success(true),
+  ),
+  http.post(`${TAURI_ENDPOINT}/get_provider_health`, () =>
+    success({
+      provider_id: "mock-provider",
+      app_type: "claude",
+      is_healthy: true,
+      consecutive_failures: 0,
+      last_success_at: null,
+      last_failure_at: null,
+      last_error: null,
+      updated_at: new Date().toISOString(),
+    }),
+  ),
+  http.post(`${TAURI_ENDPOINT}/reset_circuit_breaker`, () => success(true)),
+  http.post(`${TAURI_ENDPOINT}/get_circuit_breaker_stats`, () => success(null)),
 ];