Fix hover element on ACP thread mode selector (#38204)

Closes #38197

This will render `^ click to also ...` on MacOS and `Ctrl + click to
also ...` on Windows and Linux.

|Before|After|
|-|-|
| <img width="683" height="197" alt="image"
src="https://github.com/user-attachments/assets/09909f1b-3163-40d1-b025-4eb9b159fbf3"
/> | <img width="683" height="197" alt="image"
src="https://github.com/user-attachments/assets/47d0290d-afa2-4b1b-a588-adfe3130d0b1"
/>|

On Mac: 

<img width="683" height="197" alt="image"
src="https://github.com/user-attachments/assets/f63103b5-1ceb-4193-ae6c-be55b97106e0"
/>

Release Notes:

- Fixed keymap hint when hovering over mode selector

---------

Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/agent_ui/src/acp/mode_selector.rs

@@ -107,13 +107,15 @@ impl ModeSelector {
                                         .text_sm()
                                         .text_color(Color::Muted.color(cx))
                                         .child("Hold")
-                                        .child(div().pt_0p5().children(ui::render_modifiers(
-                                            &gpui::Modifiers::secondary_key(),
-                                            PlatformStyle::platform(),
-                                            None,
-                                            Some(ui::TextSize::Default.rems(cx).into()),
-                                            true,
-                                        )))
+                                        .child(h_flex().flex_shrink_0().children(
+                                            ui::render_modifiers(
+                                                &gpui::Modifiers::secondary_key(),
+                                                PlatformStyle::platform(),
+                                                None,
+                                                Some(ui::TextSize::Default.rems(cx).into()),
+                                                true,
+                                            ),
+                                        ))
                                         .child(div().map(|this| {
                                             if is_default {
                                                 this.child("to also unset as default")