feat: Support dark mode in login pages (#7420)

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

app/controllers/dashboard_controller.rb

@@ -1,6 +1,7 @@
 class DashboardController < ActionController::Base
   include SwitchLocale
 
+  before_action :set_application_pack
   before_action :set_global_config
   around_action :switch_locale
   before_action :ensure_installation_onboarding, only: [:index]
@@ -60,4 +61,12 @@ class DashboardController < ActionController::Base
       GIT_SHA: GIT_HASH
     }
   end
+
+  def set_application_pack
+    @application_pack = if request.path.include?('/auth') || request.path.include?('/login')
+                          'v3app'
+                        else
+                          'application'
+                        end
+  end
 end