assistant2: Wire up context picker with inline assist (#22106)

This PR wire up the context picker with the inline assist.

UI is not finalized.

Release Notes:

- N/A

---------

Co-authored-by: Richard <richard@zed.dev>
Co-authored-by: Agus <agus@zed.dev>

crates/assistant2/src/assistant_panel.rs

@@ -110,6 +110,10 @@ impl AssistantPanel {
         self.local_timezone
     }
 
+    pub(crate) fn thread_store(&self) -> &Model<ThreadStore> {
+        &self.thread_store
+    }
+
     fn new_thread(&mut self, cx: &mut ViewContext<Self>) {
         let thread = self
             .thread_store