assistant2: Show file icons for context entries (#22928)

https://github.com/user-attachments/assets/d3d6f5f1-23ec-449b-a762-9869b9d4b5a5


Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>
Co-authored-by: Michael <michael@zed.dev>

crates/assistant2/src/context_store.rs

@@ -273,6 +273,7 @@ impl ContextStore {
                 name,
                 parent,
                 tooltip: Some(full_path),
+                icon_path: None,
                 kind: ContextKind::Directory,
                 text,
             },