feat(ui): flex-wrap the ribbon top bar and status bar when narrow

Add shared adaptive-bar widgets in src/ui/wrap_bar.rs:
- WrapBar: two-block bar (lead + optional Fill middle + trail). Fits on
  one row, otherwise the trailing block drops below; with no middle both
  blocks flex-wrap in their own row bands and stack so a wrapped lead item
  never shares a row with a trailing item.
- WrapFlow: CSS-style flex-wrap row that spreads its items across as many
  rows as the width needs.

Ribbon tab row: quick-access buttons and undo/redo are merged into one
WrapFlow; the tabs are a second WrapFlow. Dropdown overlays anchor to the
measured (possibly taller) bar height instead of a hardcoded 28px.

Status bar: the hamburger menu plus the Model/layout tabs form one
WrapFlow; the status pills form another. The layout-tab scroll arrows and
horizontal scrollable are removed in favour of wrapping.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/mod.rs

@@ -15,6 +15,7 @@ pub mod statusbar;
 pub mod style;
 pub mod text_util;
 pub mod window;
+pub mod wrap_bar;
 
 pub use command_line::CommandLine;
 pub use properties::PropertiesPanel;