Forms: an option list stays inside the window; media ratios are checked in one place

The floating list under a Select, Combobox or MultiSelect was at least its
trigger's width with no ceiling, so a long choice ran it past the window
and its rows never ellipsized. It now stops at the window's width less the
window margin on each side, so gpui snaps it inside. The camera preview
and the model viewer check their ratio through primitives::checked_ratio.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/forms/options.rs

@@ -286,10 +286,12 @@ impl Popup<'_> {
             })
         });
         let list = surface(self.id, cx)
+            .debug_selector(|| "option-list".into())
             .min_w(theme.tooltip_max_width())
             .when(anchor.size.width > Pixels::ZERO, |list| {
                 list.min_w(anchor.size.width)
             })
+            .max_w(window.viewport_size().width - theme.window_margin() * 2.0)
             .max_h(theme.list_max_height())
             .overflow_y_scroll()
             .when_some(self.scroll, |list, handle| list.track_scroll(handle))