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/Utils/Database.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace App\Utils;
+
+use PDO;
+use PDOException;
+
+class Database
+{
+    private static $instance = null;
+    private $connection;
+
+    private function __construct()
+    {
+        $config = require __DIR__ . '/../../config/database.php';
+
+        $dsn = sprintf(
+            "mysql:host=%s;port=%s;dbname=%s;charset=%s",
+            $config['host'],
+            $config['port'],
+            $config['database'],
+            $config['charset']
+        );
+
+        try {
+            $this->connection = new PDO(
+                $dsn,
+                $config['username'],
+                $config['password'],
+                $config['options']
+            );
+        } catch (PDOException $e) {
+            throw new \Exception("数据库连接失败: " . $e->getMessage());
+        }
+    }
+
+    public static function getInstance()
+    {
+        if (self::$instance === null) {
+            self::$instance = new self();
+        }
+        return self::$instance;
+    }
+
+    public function getConnection()
+    {
+        return $this->connection;
+    }
+}