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/assistant_context_editor/src/slash_command_picker.rs

@@ -243,7 +243,7 @@ impl PickerDelegate for SlashCommandDelegate {
                                 Label::new(info.description.clone())
                                     .size(LabelSize::Small)
                                     .color(Color::Muted)
-                                    .text_ellipsis(),
+                                    .truncate(),
                             ),
                     ),
             ),