[#73968] Add card box item bridge

Extracts the BorderBox row arguments into a row-bridge object
(`WorkPackageCardBoxComponent::Item`) so the box can build rows without
forcing the visual card to render row-level concerns. The visual
`WorkPackageCardComponent` constructor narrows to
`(work_package:, menu_src:)`; in-repo callers updated.

Adds a polymorphic slot API (`with_work_package_item`,
`with_empty_item`) modeled on `Primer::Alpha::FileTreeView`, plus a
public `#build_item` for off-box callers. Renames the URL pass-through
to a generic `params:` kwarg, leaving Backlogs all-state handling at the
call sites.

https://community.openproject.org/wp/73968

lookbook/previews/open_project/common/work_package_card_box_component_preview.rb

@@ -32,6 +32,8 @@ module OpenProject
   module Common
     # @logical_path OpenProject/Common
     class WorkPackageCardBoxComponentPreview < ViewComponent::Preview
+      include ActionView::RecordIdentifier
+
       def sprint_with_cards
         sprint = Sprint.first
         project = sprint&.project
@@ -69,7 +71,9 @@ module OpenProject
         return preview_message("No project in the database.") unless project
 
         render OpenProject::Common::WorkPackageCardBoxComponent.new(
-          work_packages: [], project:, container: nil
+          work_packages: [],
+          project:,
+          container: dom_target(:inbox, project)
         ) do |box|
           box.with_empty_state(title: "Inbox is empty", description: "All caught up",
                                icon: :"op-backlogs")
@@ -94,7 +98,9 @@ module OpenProject
         end
 
         render OpenProject::Common::WorkPackageCardBoxComponent.new(
-          work_packages:, project:, container: nil
+          work_packages:,
+          project:,
+          container: dom_target(:inbox, project)
         ) do |box|
           box.with_empty_state(title: "Inbox is empty", description: "All caught up", icon: :"op-backlogs")
           box.with_show_more(truncate_middle: 50)

lookbook/previews/open_project/common/work_package_card_component_preview.rb

@@ -34,26 +34,10 @@ module OpenProject
     class WorkPackageCardComponentPreview < ViewComponent::Preview
       def default
         work_package = WorkPackage.first
-        project = work_package&.project
-        return preview_message("No work packages in the database.") unless work_package && project
-
-        sprint = Sprint.where(project_id: project.id).first
-        render OpenProject::Common::WorkPackageCardComponent.new(
-          work_package:,
-          project:,
-          container: sprint
-        )
-      end
-
-      def inbox_context
-        work_package = WorkPackage.first
-        project = work_package&.project
-        return preview_message("No work packages in the database.") unless work_package && project
+        return preview_message("No work packages in the database.") unless work_package
 
         render OpenProject::Common::WorkPackageCardComponent.new(
-          work_package:,
-          project:,
-          container: nil
+          work_package:
         )
       end