feat(ui): scrollable resource tabs and railpack default

Add a shared resource-heading-tabs scroller with overflow chevrons,
wire it into resource/server navbars, keep links menus outside overflow,
and default new git apps to Railpack instead of Nixpacks.

app/Livewire/Project/New/GitlabPrivateRepository.php

@@ -57,7 +57,7 @@ class GitlabPrivateRepository extends Component
 
     protected int $page = 1;
 
-    public $build_pack = 'nixpacks';
+    public $build_pack = 'railpack';
 
     public bool $show_is_static = true;