Add database connection helper and live now-playing page

- includes/db.php: getDB() returns a shared PDO connection to MariaDB
- config/db_credentials.example.php: credentials template; the real
  db_credentials.php is gitignored and deployed separately via SFTP
- live.php: page for active broadcasts, with the player on the left
  and a placeholder Recently Played table on the right

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/db_credentials.example.php

@@ -0,0 +1,18 @@
+<?php
+// Database credentials template.
+// Copy this file to db_credentials.php in the same directory and fill in real values.
+// db_credentials.php is gitignored — never commit it. Upload it to the server via SFTP separately.
+
+if (basename($_SERVER['SCRIPT_FILENAME'] ?? '') === basename(__FILE__)) {
+    http_response_code(403);
+    exit;
+}
+
+return [
+    'host'     => 'localhost',
+    'port'     => 3306,
+    'database' => '',
+    'username' => '',
+    'password' => '',
+    'charset'  => 'utf8mb4',
+];