added deployment file

docker/conn.php

@@ -0,0 +1,16 @@
+<?php
+// Docker-only replacement for includes/conn.php; local/server config is untouched.
+mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
+foreach (['MYSQL_HOST', 'MYSQL_DATABASE', 'MYSQL_USER', 'MYSQL_PASSWORD'] as $key) {
+    if (getenv($key) === false || getenv($key) === '') {
+        throw new RuntimeException('Missing database environment variable: ' . $key);
+    }
+}
+$conn = new mysqli(
+    getenv('MYSQL_HOST'),
+    getenv('MYSQL_USER'),
+    getenv('MYSQL_PASSWORD'),
+    getenv('MYSQL_DATABASE'),
+    (int) (getenv('MYSQL_PORT') ?: 3306)
+);
+$conn->set_charset('utf8mb4');