assistant: Polish /workflow and steps UI (#15936)

Fixes #15923
Release Notes:

- Assistant workflow steps can now be applied and reverted directly from
within the assistant panel.

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Antonio <antonio@zed.dev>

crates/editor/src/hunk_diff.rs

@@ -525,6 +525,7 @@ impl Editor {
                         .child(editor_with_deleted_text.clone())
                         .into_any_element()
                 }),
+                priority: 0,
             }),
             None,
             cx,