CourseHub: AJAX video course player (PHP + MySQL + Bootstrap + Plyr)

Scans nested course folders for mp4s, tracks per-user resume position
and per-folder progress. SPA frontend with hash routing over a JSON API;
range-request streaming via stream.php.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

includes/db.php

@@ -0,0 +1,16 @@
+<?php
+require_once __DIR__ . '/../config.php';
+
+function db(): PDO
+{
+    static $pdo = null;
+    if ($pdo === null) {
+        $dsn = 'mysql:host=' . DB_HOST . ';port=' . DB_PORT . ';dbname=' . DB_NAME . ';charset=utf8mb4';
+        $pdo = new PDO($dsn, DB_USER, DB_PASS, [
+            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
+            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
+            PDO::ATTR_EMULATE_PREPARES   => false,
+        ]);
+    }
+    return $pdo;
+}