agent: Refresh UI when context or thread history changes (#28188)

I found a few more cases where the UI wasn't updated immediately after
an interaction.

Release Notes:

- agent: Fixed delay after removing threads from "Past Interactions"
- agent: Fixed delay after adding/remove context via keyboard

crates/agent/src/context_picker/fetch_context_picker.rs

@@ -213,8 +213,8 @@ impl PickerDelegate for FetchContextPickerDelegate {
             this.update_in(cx, |this, window, cx| {
                 this.delegate
                     .context_store
-                    .update(cx, |context_store, _cx| {
-                        context_store.add_fetched_url(url, text);
+                    .update(cx, |context_store, cx| {
+                        context_store.add_fetched_url(url, text, cx)
                     })?;
 
                 match confirm_behavior {