Start MySQL implementation: config template, PDO layer and migrations

lib/db.php

@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+function appConfig(): array
+{
+    static $cfg = null;
+    if ($cfg !== null) {
+        return $cfg;
+    }
+
+    $path = __DIR__ . '/../config.php';
+    if (!is_file($path)) {
+        throw new RuntimeException('config.php not found. Copy config.php.example');
+    }
+
+    $cfg = require $path;
+    if (!is_array($cfg)) {
+        throw new RuntimeException('Invalid config.php format');
+    }
+
+    return $cfg;
+}
+
+function db(): PDO
+{
+    static $pdo = null;
+    if ($pdo instanceof PDO) {
+        return $pdo;
+    }
+
+    $db = appConfig()['db'] ?? [];
+    $host = $db['host'] ?? '127.0.0.1';
+    $port = (int)($db['port'] ?? 3306);
+    $name = $db['name'] ?? '';
+    $user = $db['user'] ?? '';
+    $pass = $db['pass'] ?? '';
+    $charset = $db['charset'] ?? 'utf8mb4';
+
+    $dsn = "mysql:host={$host};port={$port};dbname={$name};charset={$charset}";
+    $pdo = new PDO($dsn, (string)$user, (string)$pass, [
+        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
+        PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
+    ]);
+
+    return $pdo;
+}