Parallelize disk scanning

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/main.rs

@@ -31,7 +31,7 @@ struct Cli {
     #[arg(long)]
     verify_full: bool,
 
-    /// Number of worker threads used for hashing. Defaults to Rayon automatic sizing.
+    /// Number of worker threads used for scanning and hashing. Defaults to CPU parallelism.
     #[arg(long, value_parser = parse_thread_count)]
     threads: Option<usize>,
 
@@ -72,6 +72,7 @@ fn main() -> anyhow::Result<ExitCode> {
         hash_bytes: cli.hash_bytes,
         follow_links: cli.follow_links,
         verify_full: cli.verify_full,
+        threads: cli.threads,
     });
 
     let stdout = io::stdout();