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-basic-syntax/language-math.md

@@ -0,0 +1,28 @@
+# Math
+
+Math can be applied directly to variable values.
+
+## Examples
+```smarty
+{$foo+1}
+
+{$foo*$bar}
+
+{* some more complicated examples *}
+
+{$foo->bar-$bar[1]*$baz->foo->bar()-3*7}
+
+{if ($foo+$bar.test%$baz*134232+10+$b+10)}
+
+{$foo|truncate:"`$fooTruncCount/$barTruncFactor-1`"}
+
+{assign var="foo" value="`$foo+$bar`"}
+```
+      
+> **Note**
+>
+> Although Smarty can handle some very complex expressions and syntax,
+> it is a good rule of thumb to keep the template syntax minimal and
+> focused on presentation. If you find your template syntax getting too
+> complex, it may be a good idea to move the bits that do not deal
+> explicitly with presentation to PHP by way of plugins or modifiers.