Text styles: the panel menu's Duplicate highlights the copy and Delete clears the highlight

Squashed from #4419 onto main.

docs/target-app-parity.md

@@ -491,6 +491,7 @@ since 2026-10-01.
 - **Text styles redefined to the defaults:** New and Redefine Character Style and Paragraph Style capture every attribute of the selected text, including those at their defaults (Auto kerning, Roman baseline alignment, the default Hyphenation options, the Every-line Composer, no tab stops), and `charStyle.setAttrs` and `paraStyle.setAttrs` keep an attribute set to its default value. After a redefinition, text whose value still equals the old definition's takes the new value, a default included; local overrides and attributes the new definition leaves out stay. The style panels show "+" only where the text differs from its style, including type with Auto alignment. Public reference: [Character and paragraph styles](https://web.archive.org/web/20260825113735/https://helpx.adobe.com/illustrator/using/character-paragraph-styles.html).
 - **Text styles dragged onto the panel's buttons:** a style dragged from the Character Styles or Paragraph Styles panel onto Create New Style is copied (`charStyle.duplicate`, `paraStyle.duplicate`, which name the copy `<name> copy`) and the copy is highlighted; dragged onto Delete it is deleted (`charStyle.delete`, `paraStyle.delete`); the Normal style is not deleted. Each drop is one undo step. Public reference: [Character and paragraph styles](https://web.archive.org/web/20261015081534/https://helpx.adobe.com/illustrator/using/character-paragraph-styles.html).
 - **Auto Leading outside the layout:** a paragraph's Justification… › Auto Leading (<https://helpx.adobe.com/illustrator/desktop/design-with-text/edit-format-text/adjust-word-and-letterspacing-in-justified-text.html>) also sets the Leading the Character panel shows for Auto type (blank where the selected paragraphs differ), the leading the Alt+↑/↓ nudge (`type.step`) steps from, each paragraph's own, and the lines Fill with Placeholder Text counts in area type. Evidence: `ParaStyle::effective_leading` (`crates/doc/src/text.rs` test `paragraph_effective_leading_follows_auto_leading`), `tests_prefs::auto_leading_steps_and_fills_from_the_paragraph_auto_leading`, `panels::character` test `leading_field_shows_the_paragraph_auto_leading`.
+- **The text style panel menus' Duplicate and Delete:** in the Character Styles and Paragraph Styles panel menus, Duplicate highlights the copy, as Create New Style highlights the new style, and Delete leaves no style highlighted, as the Delete button does, so Duplicate, Clear Overrides, Redefine and Style Options are disabled until another style is clicked. A highlighted style that is renamed in Style Options or deleted by a command is no longer highlighted either. The tests `panels::text_styles::tests::panel_menu_duplicate_and_delete_update_the_highlighted_style` and `a_highlighted_style_that_is_no_longer_listed_is_not_highlighted` cover this. Public reference: [Character and paragraph styles](https://web.archive.org/web/20261015081534/https://helpx.adobe.com/illustrator/using/character-paragraph-styles.html).
 - **Names of new styles and symbols:** `charStyle.new` and `paraStyle.new` trim the white space around the name they are given, as `charStyle.rename` and `paraStyle.rename` do, and refuse a name that is then empty; Duplicate names its copy from the trimmed name. `symbol.new` and `symbol.duplicate` trim the name as Symbol Options does, and `library.use` adds a library's text style under its trimmed name. Public reference: [Character and paragraph styles](https://web.archive.org/web/20260825113735/https://helpx.adobe.com/illustrator/using/character-paragraph-styles.html).
 - **Width Point Edit:** Shift-double-click enables Adjust Adjoining Width Points; plain double-click and direct opening retain the default. Tool dispatch and headless dialog tests cover neighboring widths, Undo/Redo and Cancel. Public reference: [Variable-width strokes](https://helpx.adobe.com/illustrator/using/stroke-object.html).
 Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a feature lands.