thread_view: Fix the thinking toggle button (#59111)

We recently changed this given some new models (e.g., Fable) don't allow
turning thinking off. In those cases, we are not rendering the split
button anymore, but we should still display the thinking icon, so they
look a bit more consistent.

Release Notes:

- N/A

crates/agent_ui/src/conversation_view/thread_view.rs

@@ -4827,20 +4827,27 @@ impl ThreadView {
             }
         });
 
-        // When rendered as the right half of the split button next to the
-        // thinking toggle, only the right corners are rounded.
         let trigger = if standalone {
-            ButtonLike::new("effort-selector-trigger")
+            ButtonLike::new("effort-selector-trigger").child(
+                h_flex()
+                    .gap_1()
+                    .child(
+                        Icon::new(IconName::ThinkingMode)
+                            .size(IconSize::Small)
+                            .color(label_color),
+                    )
+                    .child(Label::new(label).size(LabelSize::Small).color(label_color))
+                    .child(Icon::new(icon).size(IconSize::XSmall).color(Color::Muted)),
+            )
         } else {
             ButtonLike::new_rounded_right("effort-selector-trigger")
+                .child(Label::new(label).size(LabelSize::Small).color(label_color))
+                .child(Icon::new(icon).size(IconSize::XSmall).color(Color::Muted))
         };
 
         PopoverMenu::new("effort-selector")
             .trigger_with_tooltip(
-                trigger
-                    .selected_style(ButtonStyle::Tinted(TintColor::Accent))
-                    .child(Label::new(label).size(LabelSize::Small).color(label_color))
-                    .child(Icon::new(icon).size(IconSize::XSmall).color(Color::Muted)),
+                trigger.selected_style(ButtonStyle::Tinted(TintColor::Accent)),
                 tooltip,
             )
             .menu(move |window, cx| {