📎 Remove a double blank line in the dashboard sidebar styles

Prettier rejects the two blank lines left after the imports, which made
the frontend lint fail in CI.

AI-assisted-by: claude-opus-5-5

frontend/src/app/main/ui/dashboard/sidebar.scss

@@ -13,7 +13,6 @@
 @use "ds/z-index.scss" as *;
 @use "ds/mixins.scss" as *;
 
-
 // refactor/ stays for the menu placeholders (%menu-dropdown,
 // %menu-item-base) of the profile menu and its submenus.
 @use "common/refactor/common-refactor.scss" as deprecated;