Ribbon key tips: Alt shows codes on tabs, buttons and menu items

A lone Alt shows a code on every ribbon tab and quick-access button.
Typing a tab code opens the tab and shows the codes of its buttons,
dropdowns, slide-outs and collapsed panels; a button code runs it, a
dropdown or slide-out code opens it and shows its item codes, Esc goes
back one level. Codes follow the reference ribbon; buttons without a
reference counterpart get none and unnamed menu items are numbered.

Codes are drawn as accent pills over the widgets that reported their
bounds in the current frame, with a hint bar under the ribbon. While
the tips are open keys go to them only. The automation gets a keytips
action and read operation.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/mod.rs

@@ -2754,6 +2754,8 @@ pub enum Message {
     SetProjection(bool),
     /// Select a ribbon module tab by index.
     RibbonSelectTab(usize),
+    /// Ribbon key tips: Alt, typed codes and Esc.
+    KeyTip(crate::ui::ribbon::KeyTipInput),
     /// Change the ribbon tool-panel density (persisted).
     SetRibbonCollapseMode(crate::ui::ribbon::CollapseMode),
     /// A ribbon tool button was clicked — highlights the tool and dispatches its event.