feat(api): 初始化笔记应用后端基础架构

- 添加环境配置文件 .env.example 包含数据库、JWT、CORS等配置
- 创建 .gitignore 文件忽略敏感文件和临时文件
- 配置 Apache 重写规则支持路由转发
- 实现 JWT 认证中间件提供用户身份验证功能
- 添加 MySQL 数据库初始化脚本包含分组、图片、笔记表结构

biji-php/src/Middleware/CorsMiddleware.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace App\Middleware;
+
+use Psr\Http\Message\ServerRequestInterface as Request;
+use Psr\Http\Server\RequestHandlerInterface as RequestHandler;
+use Slim\Psr7\Response;
+
+class CorsMiddleware
+{
+    public function __invoke(Request $request, RequestHandler $handler): Response
+    {
+        $response = $handler->handle($request);
+
+        $origin = $_ENV['CORS_ORIGIN'] ?? '*';
+
+        return $response
+            ->withHeader('Access-Control-Allow-Origin', $origin)
+            ->withHeader('Access-Control-Allow-Headers', 'X-Requested-With, Content-Type, Accept, Origin, Authorization')
+            ->withHeader('Access-Control-Allow-Methods', 'GET, POST, PUT, DELETE, PATCH, OPTIONS')
+            ->withHeader('Access-Control-Allow-Credentials', 'true');
+    }
+}