feat: add file name to fuzzy search response (#4619)

### Summary
* Updated fuzzy search result to include the file name. 
* This should not affect CLI usage and the UI there will be addressed in
a separate PR.

### Testing
Tested locally and with the extension.

### Screenshot
<img width="431" height="244" alt="Screenshot 2025-10-02 at 11 08 44 AM"
src="https://github.com/user-attachments/assets/ba2ca299-a81d-4453-9242-1750e945aea2"
/>

---------

Co-authored-by: shijie.rao <shijie.rao@squareup.com>

codex-rs/app-server-protocol/src/protocol.rs

@@ -725,6 +725,7 @@ pub struct FuzzyFileSearchParams {
 pub struct FuzzyFileSearchResult {
     pub root: String,
     pub path: String,
+    pub file_name: String,
     pub score: u32,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub indices: Option<Vec<u32>>,