agent_ui: Clear model selector query on dismiss (#37569)

Closes #36756

| Before | After |
|--------|--------|
| <video src
="https://github.com/user-attachments/assets/1d022ac6-0aea-4e98-a717-9988420c9683"/>
| <video
src="https://github.com/user-attachments/assets/78d19012-1224-4c92-a6c8-47ae4c13ca31"/>
|

Release Notes:

- agent: Clear model selector query on dismiss in agent panel

---------

Signed-off-by: Umesh Yadav <git@umesh.dev>

crates/agent_ui/src/acp/model_selector.rs

@@ -192,8 +192,10 @@ impl PickerDelegate for AcpModelPickerDelegate {
         }
     }
 
-    fn dismissed(&mut self, _: &mut Window, cx: &mut Context<Picker<Self>>) {
-        cx.emit(DismissEvent);
+    fn dismissed(&mut self, window: &mut Window, cx: &mut Context<Picker<Self>>) {
+        cx.defer_in(window, |picker, window, cx| {
+            picker.set_query("", window, cx);
+        });
     }
 
     fn render_match(