feat: highlight matching characters in fuzzy file search (#1420)

Using the new file-search API introduced in
https://github.com/openai/codex/pull/1419, matching characters are now
shown in bold in the TUI:


https://github.com/user-attachments/assets/8bbcc6c6-75a3-493f-8ea4-b2a063e09b3a

Fixes https://github.com/openai/codex/issues/1261

codex-rs/tui/src/app_event.rs

@@ -1,4 +1,5 @@
 use codex_core::protocol::Event;
+use codex_file_search::FileMatch;
 use crossterm::event::KeyEvent;
 
 use crate::slash_command::SlashCommand;
@@ -39,6 +40,6 @@ pub(crate) enum AppEvent {
     /// still relevant.
     FileSearchResult {
         query: String,
-        matches: Vec<String>,
+        matches: Vec<FileMatch>,
     },
 }