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/plugins/plugins-howto.md

@@ -0,0 +1,18 @@
+How Plugins Work {#plugins.howto}
+================
+
+Plugins are always loaded on demand. Only the specific modifiers,
+functions, resources, etc invoked in the templates scripts will be
+loaded. Moreover, each plugin is loaded only once, even if you have
+several different instances of Smarty running within the same request.
+
+Pre/postfilters and output filters are a bit of a special case. Since
+they are not mentioned in the templates, they must be registered or
+loaded explicitly via API functions before the template is processed.
+The order in which multiple filters of the same type are executed
+depends on the order in which they are registered or loaded.
+
+The [plugins directory](#variable.plugins.dir) can be a string
+containing a path or an array containing multiple paths. To install a
+plugin, simply place it in one of the directories and Smarty will use it
+automatically.