feat(proxy): implement local HTTP proxy server with multi-provider failover

Add a complete HTTP proxy server implementation built on Axum framework,
enabling local API request forwarding with automatic provider failover
and load balancing capabilities.

Backend Implementation (Rust):
- Add proxy server module with 7 core components:
  * server.rs: Axum HTTP server lifecycle management (start/stop/status)
  * router.rs: API routing configuration for Claude/OpenAI/Gemini endpoints
  * handlers.rs: Request/response handling and transformation
  * forwarder.rs: Upstream forwarding logic with retry mechanism (652 lines)
  * error.rs: Comprehensive error handling and HTTP status mapping
  * types.rs: Shared types (ProxyConfig, ProxyStatus, ProxyServerInfo)
  * health.rs: Provider health check infrastructure

Service Layer:
- Add ProxyService (services/proxy.rs, 157 lines):
  * Manage proxy server lifecycle
  * Handle configuration updates
  * Track runtime status and metrics

Database Layer:
- Add proxy configuration DAO (dao/proxy.rs, 242 lines):
  * Persist proxy settings (listen address, port, timeout)
  * Store provider priority and availability flags
- Update schema with proxy_config table (schema.rs):
  * Support runtime configuration persistence

Tauri Commands:
- Add 6 command endpoints (commands/proxy.rs):
  * start_proxy_server: Launch proxy server
  * stop_proxy_server: Gracefully shutdown server
  * get_proxy_status: Query runtime status
  * get_proxy_config: Retrieve current configuration
  * update_proxy_config: Modify settings without restart
  * is_proxy_running: Check server state

Frontend Implementation (React + TypeScript):
- Add ProxyPanel component (222 lines):
  * Real-time server status display
  * Start/stop controls
  * Provider availability monitoring
- Add ProxySettingsDialog component (420 lines):
  * Configuration editor (address, port, timeout)
  * Provider priority management
  * Settings validation
- Add React hooks:
  * useProxyConfig: Manage proxy configuration state
  * useProxyStatus: Poll and display server status
- Add TypeScript types (types/proxy.ts):
  * Define ProxyConfig, ProxyStatus interfaces

Provider Integration:
- Extend Provider model with availability field (providers.rs):
  * Track provider health for failover logic
- Update ProviderCard UI to display proxy status
- Integrate proxy controls in Settings page

Dependencies:
- Add Axum 0.7 (async web framework)
- Add Tower 0.4 (middleware and service abstractions)
- Add Tower-HTTP (CORS layer)
- Add Tokio sync primitives (oneshot, RwLock)

Technical Details:
- Graceful shutdown via oneshot channel
- Shared state with Arc<RwLock<T>> for thread-safe config updates
- CORS enabled for cross-origin frontend access
- Request/response streaming support
- Automatic retry with exponential backoff (forwarder)
- API key extraction from multiple config formats (Claude/Codex/Gemini)

File Statistics:
- 41 files changed
- 3491 insertions(+), 41 deletions(-)
- Core modules: 1393 lines (server + forwarder + handlers)
- Frontend UI: 642 lines (ProxyPanel + ProxySettingsDialog)
- Database/DAO: 326 lines

This implementation provides the foundation for advanced features like:
- Multi-provider load balancing
- Automatic failover on provider errors
- Request logging and analytics
- Usage tracking and cost monitoring

src/hooks/useProxyConfig.ts

@@ -0,0 +1,42 @@
+/**
+ * 代理配置管理 Hook
+ */
+
+import { useQuery, useMutation, useQueryClient } from "@tanstack/react-query";
+import { invoke } from "@tauri-apps/api/core";
+import { toast } from "sonner";
+import type { ProxyConfig } from "@/types/proxy";
+
+/**
+ * 代理配置管理
+ */
+export function useProxyConfig() {
+  const queryClient = useQueryClient();
+
+  // 查询配置
+  const { data: config, isLoading } = useQuery({
+    queryKey: ["proxyConfig"],
+    queryFn: () => invoke<ProxyConfig>("get_proxy_config"),
+  });
+
+  // 更新配置
+  const updateMutation = useMutation({
+    mutationFn: (newConfig: ProxyConfig) =>
+      invoke("update_proxy_config", { config: newConfig }),
+    onSuccess: () => {
+      toast.success("代理配置已保存");
+      queryClient.invalidateQueries({ queryKey: ["proxyConfig"] });
+      queryClient.invalidateQueries({ queryKey: ["proxyStatus"] });
+    },
+    onError: (error: Error) => {
+      toast.error(`保存失败: ${error.message}`);
+    },
+  });
+
+  return {
+    config,
+    isLoading,
+    updateConfig: updateMutation.mutateAsync,
+    isUpdating: updateMutation.isPending,
+  };
+}