feat(richtext): attachment-editor List/Text format menus + text-only selection state

Add a List action to the attachment/article editor's selection toolbar, gated on a new EditorState.selectionIsTextOnly (true when the selection covers no media/table block). Make the add-menu "Text" item a normalize-to-plain-body action that strips the enclosing block container (quote/code/list/pull-quote) or heading, shown only when there is no selection or the selection is not already plain body. Extract the shared list-marker picker into presentListMenu. Adds the RichTextEditorCoreDocument typealias used by the screen. Covered by EditorStateTests + EditorFormatFacadeTests.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>