feat(admin): add transparent debug error-log mode

Add an admin-controlled debug mode that captures PHP errors of all
players into var/log/debug-players.log, to hunt remaining PHP 8.3 bugs
from real play sessions. Fully transparent to players: no redirect, no
gameplay change, errors are never displayed.

- DB: new debug_log table (one row), mirroring the maintenance pattern.
- Database: getDebugMode()/setDebugMode()/setDebugSettings(), defensive
  when the table is absent (no blank page).
- Session: register a custom error + shutdown handler when enabled; the
  handler runs even when php.ini error_reporting masks warnings/notices,
  so capture is complete without a Docker rebuild. Auto-disables after a
  configurable window.
- DebugErrorLogger: size-capped file with a single .log.1 rotation,
  honours the @ operator, never throws.
- Admin: new "Debug Error Log" page (levels, size cap, auto-off, on-page
  viewer, clear, download) + debugLog action mod.
- Menu: admin-only quick on/off widget (TZ_DEBUG_ON/OFF, EN/FR/RO).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Templates/menu.tpl

@@ -195,6 +195,11 @@ $idUser      = isset($_SESSION['id_user']) ? (int)$_SESSION['id_user'] : 0;
 		*/
 		include("Templates/maintenance_status.tpl");
 
+		/**
+		* Debug Error Log quick toggle for admins
+		*/
+		include("Templates/debug_status.tpl");
+
         ?>
 
     </p>