agent: Handle context servers that do not provide a configuration in MCP setup dialog (#30023)

<img width="674" alt="image"
src="https://github.com/user-attachments/assets/0ccb89e2-1dc1-4caf-88a7-49159f43979f"
/>
<img width="675" alt="image"
src="https://github.com/user-attachments/assets/790e5d45-905e-45da-affa-04ddd1d33c65"
/>

Release Notes:

- N/A

crates/ui/src/components/modal.rs

@@ -253,7 +253,7 @@ impl RenderOnce for ModalFooter {
             .mt_4()
             .p(DynamicSpacing::Base08.rems(cx))
             .flex_none()
-            .justify_end()
+            .justify_between()
             .gap_1()
             .border_t_1()
             .border_color(cx.theme().colors().border_variant)