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/story/src/story.rs

@@ -64,7 +64,7 @@ impl Story {
             .p_2()
             .max_w(rems(36.))
             .bg(DefaultColor::Container.hsla(&colors))
-            .rounded_md()
+            .rounded_sm()
             .text_sm()
             .text_color(DefaultColor::Text.hsla(&colors))
             .overflow_hidden()
@@ -151,7 +151,7 @@ impl RenderOnce for StoryItem {
                     .child(Story::label(self.label))
                     .child(
                         div()
-                            .rounded_md()
+                            .rounded_sm()
                             .bg(DefaultColor::Background.hsla(&colors))
                             .border_1()
                             .border_color(DefaultColor::Border.hsla(&colors))