feat(ribbon): shrink large tools to compact icons when the ribbon is narrow

Add a DensitySwap widget that renders the widest variant of the tool
area that fits the current width. The ribbon builds two variants via the
new build_tool_row(compact) helper: full-size panels, and a compact one
where LargeTool/LargeDropdown collapse to small icon columns (the
layer/properties/style combos always stay full). render_small now also
matches the Large* variants so they can be drawn small.

First stage of the adaptive tool area (shrink -> wrap -> collapse).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/ui/ribbon/widgets.rs

@@ -344,7 +344,9 @@ pub(super) fn render_small<'a>(
     ortho_mode: bool,
 ) -> Element<'a, Message> {
     match item {
-        RibbonItem::Tool(t) => {
+        // Large variants render small too, so the ribbon can shrink a panel of
+        // large buttons to icon-only columns when the width is tight.
+        RibbonItem::Tool(t) | RibbonItem::LargeTool(t) => {
             let active = is_active_tool(t.id, active_tool, wireframe, ortho_mode);
             let event = t.event.clone();
             let tool_id = t.id.to_string();
@@ -368,6 +370,13 @@ pub(super) fn render_small<'a>(
             items,
             default,
             ..
+        }
+        | RibbonItem::LargeDropdown {
+            id,
+            icon,
+            items,
+            default,
+            ..
         } => {
             let active = active_tool.as_deref() == Some(*id)
                 || items