gpui: Rename rounded_md to rounded_sm (#26228)

This PR renames the `rounded_md` style method to `rounded_sm`.

Follow up to https://github.com/zed-industries/zed/pull/26221, which
freed up the `rounded_sm` name.

Release Notes:

- N/A

crates/assistant2/src/active_thread.rs

@@ -645,7 +645,7 @@ impl ActiveThread {
             Role::System => div().id(("message-container", ix)).py_1().px_2().child(
                 v_flex()
                     .bg(colors.editor_background)
-                    .rounded_md()
+                    .rounded_sm()
                     .child(message_content),
             ),
         };

crates/assistant2/src/assistant_configuration.rs

@@ -134,7 +134,7 @@ impl AssistantConfiguration {
                     .bg(cx.theme().colors().editor_background)
                     .border_1()
                     .border_color(cx.theme().colors().border_variant)
-                    .rounded_md()
+                    .rounded_sm()
                     .map(|parent| match configuration_view {
                         Some(configuration_view) => parent.child(configuration_view),
                         None => parent.child(div().child(Label::new(format!(

crates/assistant2/src/ui/context_pill.rs

@@ -103,7 +103,7 @@ impl RenderOnce for ContextPill {
             .pl_1()
             .pb(px(1.))
             .border_1()
-            .rounded_md()
+            .rounded_sm()
             .gap_1()
             .child(self.icon().size(IconSize::XSmall).color(Color::Muted));