fix: 更换后端端口 9949 -> 18080 解决 Windows 绑定权限问题

- 修改后端默认端口为 18080
- 更新前端 API 配置支持新端口
- 更新启动/停止脚本端口配置
- 添加 .env 配置文件

script/start.bat

@@ -4,7 +4,7 @@ echo === ProxyPool Startup ===
 echo.
 
 set "ROOT_PATH=%~dp0.."
-set "BACKEND_PORT=9949"
+set "BACKEND_PORT=18080"
 set "FRONTEND_PORT=9948"
 
 REM 1. Clean processes on ports
@@ -53,7 +53,7 @@ ping -n 3 127.0.0.1 >nul 2>&1
 set /a RETRY_COUNT+=1
 
 REM Try to connect to backend health endpoint
-powershell -Command "try { $r = Invoke-RestMethod -Uri 'http://127.0.0.1:9949/health' -TimeoutSec 2 -ErrorAction Stop; exit 0 } catch { exit 1 }" >nul 2>&1
+powershell -Command "try { $r = Invoke-RestMethod -Uri 'http://127.0.0.1:18080/health' -TimeoutSec 2 -ErrorAction Stop; exit 0 } catch { exit 1 }" >nul 2>&1
 if %errorlevel% equ 0 (
     set BACKEND_READY=1
     goto WAIT_DONE
@@ -81,7 +81,7 @@ echo   Frontend started
 echo.
 
 echo === All services started ===
-echo Backend: http://127.0.0.1:9949
+echo Backend: http://127.0.0.1:18080
 echo Frontend: http://localhost:9948
 echo.
 echo Press any key to close this window (services will keep running).

script/stop.bat

@@ -3,7 +3,7 @@ chcp 65001 >nul
 echo === Stopping ProxyPool Services ===
 echo.
 
-set "BACKEND_PORT=9949"
+set "BACKEND_PORT=18080"
 set "FRONTEND_PORT=9948"
 set "STOPPED_COUNT=0"