Fix DHCP client unable to get IP and config not persisting

- Fixed verifyAssignment being too strict for new clients
- Fixed parseRequestedIP string conversion bug
- Fixed response sent to 0.0.0.0 instead of broadcast address
- Added SO_BROADCAST support for UDP socket
- Fixed session persistence after page refresh (localStorage)
- Added in-memory session store for auth middleware
- Added config reloader so DHCP server picks up web UI changes dynamically

start.bat

@@ -0,0 +1,57 @@
+#!/bin/bash
+
+# DHCP & DNS 管理器 - Windows 启动脚本
+# 适用于没有 Docker 的 Windows 环境
+
+@echo off
+echo ========================================
+echo   DHCP ^& DNS 管理器 - Windows 启动脚本
+echo ========================================
+echo.
+
+REM 检查 Go 是否安装
+where go >nul 2>nul
+if %ERRORLEVEL% NEQ 0 (
+    echo [错误] 未检测到 Go 环境
+    echo.
+    echo 请先安装 Go: https://golang.org/dl/
+    echo 或改用 Docker Desktop: https://www.docker.com/products/docker-desktop
+    pause
+    exit /b 1
+)
+
+echo [信息] Go 环境已检测
+echo.
+
+REM 创建数据目录
+if not exist "data" mkdir data
+if not exist "configs" mkdir configs
+
+REM 检查配置文件
+if not exist "configs\config.json" (
+    echo [警告] 配置文件不存在，请编辑 configs\config.json
+    echo.
+)
+
+REM 下载依赖
+echo [信息] 下载 Go 依赖...
+go mod download
+if %ERRORLEVEL% NEQ 0 (
+    echo [错误] 依赖下载失败
+    pause
+    exit /b 1
+)
+
+echo [信息] 启动服务...
+echo.
+echo 访问地址：http://localhost:8080
+echo 默认账号：admin / admin
+echo.
+echo 按 Ctrl+C 停止服务
+echo ========================================
+echo.
+
+REM 运行程序
+go run ./cmd -config configs\config.json
+
+pause