Dev-Umgebung: Kompatibilität für PHP 8.3 + Smarty 4.5.6

- Smarty 4.1.1 → 4.5.6 (behebt dynamic property deprecations)
- Core-Klassen: #[\AllowDynamicProperties] für Admin_role, base, Config,
  Customer, Customer_group, CustomerGroups, Item, Structure, website
- website.class.php: counts[parent_id] initialisieren vor ++ (PHP 8.1)
- layout.class.php: HTTP_ACCEPT_LANGUAGE mit isset-Guard
- website_init.php: session_status()-Check vor session_start
- .htaccess: HTTPS-Redirect via X-Forwarded-Proto (statt SERVER_PORT)
- themes/easyshop_advanced/media/: Parent-Theme-Assets nachgezogen
- .gitignore: smarty.4.1.1.bak ausschließen

libs/smarty/docs/programmers/api-functions/api-mute-expected-errors.md

@@ -0,0 +1,21 @@
+Smarty::muteExpectedErrors()
+
+mutes expected warnings and notices deliberately generated by Smarty
+
+Description
+===========
+
+string
+
+muteExpectedErrors
+
+muteExpectedErrors() registers a custom error handler using
+[set\_error\_handler()](https://www.php.net/set_error_handler). The error
+handler merely inspects `$errno` and `$errfile` to determine if the
+given error was produced deliberately and must be ignored, or should be
+passed on to the next error handler.
+
+`Smarty::unmuteExpectedErrors()` removes the current error handler.
+Please note, that if you\'ve registered any custom error handlers after
+the muteExpectedErrors() call, the unmute will not remove Smarty\'s
+muting error handler, but the one registered last.