Initial support for AI assistant rules files (#27168)

Release Notes:

- N/A

---------

Co-authored-by: Danilo <danilo@zed.dev>
Co-authored-by: Nathan <nathan@zed.dev>
Co-authored-by: Thomas <thomas@zed.dev>

crates/assistant_eval/src/eval.rs

@@ -79,10 +79,25 @@ impl Eval {
 
             let start_time = std::time::SystemTime::now();
 
+            let (system_prompt_context, load_error) = cx
+                .update(|cx| {
+                    assistant
+                        .read(cx)
+                        .thread
+                        .read(cx)
+                        .load_system_prompt_context(cx)
+                })?
+                .await;
+
+            if let Some(load_error) = load_error {
+                return Err(anyhow!("{:?}", load_error));
+            };
+
             assistant.update(cx, |assistant, cx| {
                 assistant.thread.update(cx, |thread, cx| {
                     let context = vec![];
                     thread.insert_user_message(self.user_prompt.clone(), context, None, cx);
+                    thread.set_system_prompt_context(system_prompt_context);
                     thread.send_to_model(model, RequestKind::Chat, cx);
                 });
             })?;