assistant2: Add design refinements (#27160)

Release Notes:

- N/A

---------

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Agus Zubiaga <hi@aguz.me>

crates/git_ui/src/git_panel.rs

@@ -2786,7 +2786,7 @@ impl GitPanel {
                     panel_button(change_string)
                         .color(Color::Muted)
                         .tooltip(Tooltip::for_action_title_in(
-                            "Open diff",
+                            "Open Diff",
                             &Diff,
                             &self.focus_handle,
                         ))