fix: harden billing module for standalone portability

- config_loader.php: prefer local billing config FIRST (root cause fix)
  - was: panel config loaded first, overriding local config with wrong db name
  - now: local modules/billing/includes/config.inc.php always wins when present
- config.inc.php: add $db_port="3306"
- config.example.php: new example config with all variables documented
- menu.php: add $db_port to mysqli_connect
- admin_auth.php: add $db_port; remove hardcoded /_website path detection
- bootstrap.php billing_get_db(): add $db_port
- login.php: fix /_website path detection
- adminserverlist.php: add $db_port; fix hardcoded /modules/billing/ URL
- All other mysqli_connect calls: add isset($db_port) port parameter
  (my_servers, forgot_password, serverlist, server_status, order, register,
   reset_password, payment_success, my_account, admin_invoices, admin_payments,
   diag_remote, admin_coupons, test_db_connection, tools/check_db_user,
   renew_server)
- timestamp.txt: updated

Agent-Logs-Url: https://github.com/GameServerPanel/GSP/sessions/a3e1e4bb-8eb1-4e6e-b1f8-7f3952301231

Co-authored-by: iaretechnician <2749183+iaretechnician@users.noreply.github.com>

modules/billing/renew_server.php

@@ -19,7 +19,7 @@ require_once(__DIR__ . '/includes/log.php');
 /** @var string $table_prefix Table prefix for database tables */
 
 // Connect to DB (use mysqli like other website modules)
-$db = @mysqli_connect($db_host, $db_user, $db_pass, $db_name);
+$db = @mysqli_connect($db_host, $db_user, $db_pass, $db_name, isset($db_port) ? (int)$db_port : null);
 if (!$db) {
     // fail silently and redirect back
     $back = $_SERVER['HTTP_REFERER'] ?? 'my_account.php';