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/components/proxy/ProxyPanel.tsx

@@ -0,0 +1,222 @@
+import { useState } from "react";
+import { Switch } from "@/components/ui/switch";
+import { Badge } from "@/components/ui/badge";
+import { Button } from "@/components/ui/button";
+import { useProxyStatus } from "@/hooks/useProxyStatus";
+import { Settings, Activity, Clock, TrendingUp, Server } from "lucide-react";
+import { ProxySettingsDialog } from "./ProxySettingsDialog";
+import { toast } from "sonner";
+
+export function ProxyPanel() {
+  const { status, isRunning, start, stop, isPending } = useProxyStatus();
+  const [showSettings, setShowSettings] = useState(false);
+
+  const handleToggle = async () => {
+    try {
+      if (isRunning) {
+        await stop();
+      } else {
+        await start();
+      }
+    } catch (error) {
+      console.error("Toggle proxy failed:", error);
+    }
+  };
+
+  const formatUptime = (seconds: number): string => {
+    const hours = Math.floor(seconds / 3600);
+    const minutes = Math.floor((seconds % 3600) / 60);
+    const secs = seconds % 60;
+
+    if (hours > 0) {
+      return `${hours}h ${minutes}m ${secs}s`;
+    } else if (minutes > 0) {
+      return `${minutes}m ${secs}s`;
+    } else {
+      return `${secs}s`;
+    }
+  };
+
+  return (
+    <>
+      <section className="space-y-6 rounded-xl border border-white/10 glass-card p-6">
+        <div className="flex items-center justify-between gap-4">
+          <div className="flex items-center gap-3">
+            <div className="p-2 rounded-lg bg-primary/10 text-primary">
+              <Server className="h-5 w-5" />
+            </div>
+            <div>
+              <h3 className="text-base font-semibold text-foreground">
+                本地代理服务
+              </h3>
+              <p className="text-sm text-muted-foreground">
+                {isRunning
+                  ? `运行中 · ${status?.address}:${status?.port}`
+                  : "已停止"}
+              </p>
+            </div>
+          </div>
+          <div className="flex items-center gap-3">
+            <Badge
+              variant={isRunning ? "default" : "secondary"}
+              className="gap-1.5"
+            >
+              <Activity
+                className={`h-3 w-3 ${isRunning ? "animate-pulse" : ""}`}
+              />
+              {isRunning ? "运行中" : "已停止"}
+            </Badge>
+            <Button
+              variant="ghost"
+              size="icon"
+              onClick={() => setShowSettings(true)}
+              disabled={isPending}
+              aria-label="打开代理设置"
+            >
+              <Settings className="h-4 w-4" />
+            </Button>
+            <Switch
+              checked={isRunning}
+              onCheckedChange={handleToggle}
+              disabled={isPending}
+              aria-label={isRunning ? "停止代理服务" : "启动代理服务"}
+            />
+          </div>
+        </div>
+
+        {isRunning && status ? (
+          <div className="space-y-6">
+            <div className="rounded-lg border border-white/10 bg-muted/40 p-4 space-y-4">
+              <div>
+                <p className="text-xs font-medium text-muted-foreground uppercase tracking-wide">
+                  服务地址
+                </p>
+                <div className="mt-2 flex flex-col gap-2 sm:flex-row sm:items-center">
+                  <code className="flex-1 text-sm bg-background px-3 py-2 rounded border border-border/60">
+                    http://{status.address}:{status.port}
+                  </code>
+                  <Button
+                    size="sm"
+                    variant="outline"
+                    onClick={() => {
+                      navigator.clipboard.writeText(
+                        `http://${status.address}:${status.port}`,
+                      );
+                      toast.success("地址已复制");
+                    }}
+                  >
+                    复制
+                  </Button>
+                </div>
+              </div>
+
+              <div className="pt-3 border-t border-white/10 space-y-2">
+                <p className="text-xs font-medium text-muted-foreground uppercase tracking-wide">
+                  当前代理
+                </p>
+                {status.active_targets && status.active_targets.length > 0 ? (
+                  <div className="grid gap-2 sm:grid-cols-2">
+                    {status.active_targets.map((target) => (
+                      <div
+                        key={target.app_type}
+                        className="flex items-center justify-between rounded-md border border-white/10 bg-background/60 px-2 py-1.5 text-xs"
+                      >
+                        <span className="text-muted-foreground">
+                          {target.app_type}
+                        </span>
+                        <span
+                          className="ml-2 font-medium truncate text-foreground"
+                          title={target.provider_name}
+                        >
+                          {target.provider_name}
+                        </span>
+                      </div>
+                    ))}
+                  </div>
+                ) : status.current_provider ? (
+                  <p className="text-sm text-muted-foreground">
+                    当前 Provider：{" "}
+                    <span className="font-medium text-foreground">
+                      {status.current_provider}
+                    </span>
+                  </p>
+                ) : (
+                  <p className="text-sm text-yellow-600 dark:text-yellow-400">
+                    当前 Provider：等待首次请求…
+                  </p>
+                )}
+              </div>
+            </div>
+
+            <div className="grid gap-3 md:grid-cols-4">
+              <StatCard
+                icon={<Activity className="h-4 w-4" />}
+                label="活跃连接"
+                value={status.active_connections}
+              />
+              <StatCard
+                icon={<TrendingUp className="h-4 w-4" />}
+                label="总请求数"
+                value={status.total_requests}
+              />
+              <StatCard
+                icon={<Clock className="h-4 w-4" />}
+                label="成功率"
+                value={`${status.success_rate.toFixed(1)}%`}
+                variant={status.success_rate > 90 ? "success" : "warning"}
+              />
+              <StatCard
+                icon={<Clock className="h-4 w-4" />}
+                label="运行时间"
+                value={formatUptime(status.uptime_seconds)}
+              />
+            </div>
+          </div>
+        ) : (
+          <div className="text-center py-10 text-muted-foreground">
+            <div className="mx-auto w-16 h-16 rounded-full bg-muted flex items-center justify-center mb-4">
+              <Server className="h-8 w-8" />
+            </div>
+            <p className="text-base font-medium text-foreground mb-1">
+              代理服务已停止
+            </p>
+            <p className="text-sm text-muted-foreground">
+              使用右上角开关即可启动服务
+            </p>
+          </div>
+        )}
+      </section>
+
+      <ProxySettingsDialog open={showSettings} onOpenChange={setShowSettings} />
+    </>
+  );
+}
+
+interface StatCardProps {
+  icon: React.ReactNode;
+  label: string;
+  value: string | number;
+  variant?: "default" | "success" | "warning";
+}
+
+function StatCard({ icon, label, value, variant = "default" }: StatCardProps) {
+  const variantStyles = {
+    default: "",
+    success: "border-green-500/40 bg-green-500/5",
+    warning: "border-yellow-500/40 bg-yellow-500/5",
+  };
+
+  return (
+    <div
+      className={`rounded-lg border border-white/10 bg-white/70 p-4 text-sm text-muted-foreground dark:bg-white/5 ${variantStyles[variant]}`}
+    >
+      <div className="flex items-center gap-2 text-muted-foreground mb-2">
+        {icon}
+        <span className="text-xs font-medium uppercase tracking-wide">
+          {label}
+        </span>
+      </div>
+      <p className="text-xl font-semibold text-foreground">{value}</p>
+    </div>
+  );
+}