feat: standalone file search CLI (#1386)

Standalone fuzzy filename search library that should be helpful in
addressing https://github.com/openai/codex/issues/1261.

codex-rs/file-search/src/main.rs

@@ -0,0 +1,50 @@
+use std::path::Path;
+
+use clap::Parser;
+use codex_file_search::Cli;
+use codex_file_search::Reporter;
+use codex_file_search::run_main;
+use serde_json::json;
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    let cli = Cli::parse();
+    let reporter = StdioReporter {
+        write_output_as_json: cli.json,
+    };
+    run_main(cli, reporter).await?;
+    Ok(())
+}
+
+struct StdioReporter {
+    write_output_as_json: bool,
+}
+
+impl Reporter for StdioReporter {
+    fn report_match(&self, file: &str, score: u32) {
+        if self.write_output_as_json {
+            let value = json!({ "file": file, "score": score });
+            println!("{}", serde_json::to_string(&value).unwrap());
+        } else {
+            println!("{file}");
+        }
+    }
+
+    fn warn_matches_truncated(&self, total_match_count: usize, shown_match_count: usize) {
+        if self.write_output_as_json {
+            let value = json!({"matches_truncated": true});
+            println!("{}", serde_json::to_string(&value).unwrap());
+        } else {
+            eprintln!(
+                "Warning: showing {shown_match_count} out of {total_match_count} results. Provide a more specific pattern or increase the --limit.",
+            );
+        }
+    }
+
+    fn warn_no_search_pattern(&self, search_directory: &Path) {
+        eprintln!(
+            "No search pattern specified. Showing the contents of the current directory ({}):",
+            search_directory.to_string_lossy()
+        );
+    }
+}