chore: add shared argument definitions for menu and modal features

Adds new shared argument definitions to support menu and modal functionality across
components. Updates the plain argument description to clarify its broader usage beyond
images.

Additions:
- menu: Site menu name parameter (default: main)
- menu-entry: Menu item entry object for navigation
- menu-parent: Parent menu item reference for hierarchical menus
- menu-style: Menu layout style selector (grid/masonry)
- modal: Modal control target for toggling modals

Updates:
- plain: Expanded description to cover navbar items ignoring children
- Minor whitespace cleanup for consistency

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: markdumay

data/structures/_arguments.yml

@@ -792,6 +792,31 @@ arguments:
     type: string
     optional: true
     comment: ID of the asset to be embedded.
+  menu:
+    type: string
+    optional: true
+    default: main
+    comment: Name of the site menu.
+  menu-entry:
+    type:
+      - '*navigation.MenuEntry'
+      - 'map[string]interface {}'
+    comment: Current menu item.
+  menu-parent:
+    type:
+      - '*navigation.MenuEntry'
+      - 'map[string]interface {}'
+    optional: true
+    comment: Parent of the current menu item.
+  menu-style:
+    type: select
+    optional: true
+    default: masonry
+    comment: Style of the menu layout.
+    options:
+      values:
+        - grid
+        - masonry
   min:
     type: int
     optional: true
@@ -812,6 +837,11 @@ arguments:
     optional: false
     comment: Message to display.
     group: partial
+  modal:
+    type: string
+    optional: true
+    comment: >-
+      If set, toggles a modal control for the provided target.
   mode:
     type: bool
     default: false
@@ -999,8 +1029,9 @@ arguments:
     default: false
     optional: true
     comment:
-      Flag to indicate if the image should render a plain image instead of an
-      image set. When set, no transformations are applied to the image.
+      Flag to indicate if the current element should be rendered as plain. For
+      image, this implies no transformations are applied. For navbar items,
+      this ignores any children.
   popup:	
     type: string
     optional: true
@@ -1189,7 +1220,7 @@ arguments:
     optional: true
     default: true
     comment: Indicates if the preview should be output in the HTML.
-  size: 
+  size:
     type: int
     optional: true
     config: style.title.size