IONOS(theming): fix dynamic copyright year in guest footer

- Add --current-year CSS variable (set from date('Y') in IonosTheme::getCSSVariables())
  so the guest-page footer copyright year is not hardcoded
- Use content: '© ' var(--current-year) ' IONOS SE' in guest.css

Signed-off-by: Tatjana Kaschperko Lindt <kaschperko-lindt@strato.de>
Assisted-by: ClaudeCode:claude-sonnet-4-6

Author: tanyaka

apps/theming/css/ionos/guest.css

@@ -13,7 +13,8 @@
  * bottom of the viewport instead of appearing as an inline chip.
  *
  * The footer text "HiDrive Next" (getShortFooter entity) is replaced
- * with "© YEAR IONOS SE" via a CSS pseudo-element. The slogan is set to
+ * with "© YEAR IONOS SE" via a CSS pseudo-element; the year comes from the
+ * --current-year CSS variable set in IonosTheme::getCSSVariables(). The slogan is set to
  * empty in nc-config so getShortFooter() only renders the entity <a>.
  * The href still points to the configured ionos_homepage URL.
  */
@@ -36,7 +37,7 @@ body#body-login footer.guest-box p.info a.entity-name {
 }
 
 body#body-login footer.guest-box p.info a.entity-name::before {
-    content: '© 2026 IONOS SE';
+    content: '© ' var(--current-year) ' IONOS SE';
     font-size: var(--default-font-size, 14px);
     color: var(--color-text-maxcontrast);
 }

apps/theming/lib/Themes/IonosTheme.php

@@ -274,6 +274,7 @@ public function getCSSVariables(): array {
 			'--background-invert-if-bright' => 'invert(100%)',
 			'--background-image-invert-if-bright' => 'no',
 			'--background-image-color-text' => '#ffffff',
+			'--current-year' => '"' . date('Y') . '"',
 		];
 
 		return array_merge(