git_ui: Prevent button overflow due to long names (#25940)

- Fix component preview widths for git panel
- Fix buttons getting pushed off the screen in git  panel

Release Notes:

- N/A

---------

Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>

crates/ui/src/components/button/button.rs

@@ -97,6 +97,7 @@ pub struct Button {
     key_binding: Option<KeyBinding>,
     key_binding_position: KeybindingPosition,
     alpha: Option<f32>,
+    truncate: bool,
 }
 
 impl Button {
@@ -123,6 +124,7 @@ impl Button {
             key_binding: None,
             key_binding_position: KeybindingPosition::default(),
             alpha: None,
+            truncate: false,
         }
     }
 
@@ -206,6 +208,15 @@ impl Button {
         self.alpha = Some(alpha);
         self
     }
+
+    /// Truncates overflowing labels with an ellipsis (`…`) if needed.
+    ///
+    /// Buttons with static labels should _never_ be truncated, ensure
+    /// this is only used when the label is dynamic and may overflow.
+    pub fn truncate(mut self, truncate: bool) -> Self {
+        self.truncate = truncate;
+        self
+    }
 }
 
 impl Toggleable for Button {
@@ -437,7 +448,8 @@ impl RenderOnce for Button {
                                 .color(label_color)
                                 .size(self.label_size.unwrap_or_default())
                                 .when_some(self.alpha, |this, alpha| this.alpha(alpha))
-                                .line_height_style(LineHeightStyle::UiLabel),
+                                .line_height_style(LineHeightStyle::UiLabel)
+                                .when(self.truncate, |this| this.truncate()),
                         )
                         .children(self.key_binding),
                 )