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/designers/language-builtin-functions/language-function-extends.md

@@ -0,0 +1,37 @@
+# {extends}
+
+`{extends}` tags are used in child templates in template inheritance for
+extending parent templates. For details see section of [Template
+Inheritance](../../programmers/advanced-features/advanced-features-template-inheritance.md).
+
+-   The `{extends}` tag must be on the first line of the template.
+
+-   If a child template extends a parent template with the `{extends}`
+    tag it may contain only `{block}` tags. Any other template content
+    is ignored.
+
+-   Use the syntax for [template resources](../../programmers/resources.md) to extend files
+    outside the [`$template_dir`](../../programmers/api-variables/variable-template-dir.md) directory.
+
+## Attributes
+
+| Attribute | Required | Description                                     |
+|-----------|----------|-------------------------------------------------|
+| file      | Yes      | The name of the template file which is extended |
+
+> **Note**
+>
+> When extending a variable parent like `{extends file=$parent_file}`,
+> make sure you include `$parent_file` in the
+> [`$compile_id`](../../programmers/api-variables/variable-compile-id.md). Otherwise, Smarty cannot
+> distinguish between different `$parent_file`s.
+
+## Examples
+
+```smarty
+{extends file='parent.tpl'}
+{extends 'parent.tpl'}  {* short-hand *}
+```
+
+See also [Template Inheritance](../../programmers/advanced-features/advanced-features-template-inheritance.md)
+and [`{block}`](./language-function-block.md).