feat: add search term to thread list (#12578)

Add `searchTerm` to `thread/list` that will search for a match in the
titles (the condition being `searchTerm` $$\in$$ `title`)

codex-rs/debug-client/src/client.rs

@@ -181,6 +181,7 @@ impl AppServerClient {
                 source_kinds: None,
                 archived: None,
                 cwd: None,
+                search_term: None,
             },
         };
         self.send(&request)?;