Run UCI by default

src/main.rs

@@ -13,7 +13,7 @@ use interface::uci;
 #[command(version, about, long_about = None)]
 struct Args {
     #[arg(short, long)]
-    mode: Mode,
+    mode: Option<Mode>,
 }
 
 #[derive(ValueEnum, Debug, Clone, Copy)]
@@ -26,8 +26,8 @@ fn main() {
     movegen::attack_generator::init_attacks();
 
     match Args::parse().mode {
-        Mode::Perft => search::perft::perftree_script(),
-        Mode::Uci => {
+        Some(Mode::Perft) => search::perft::perftree_script(),
+        Some(Mode::Uci) | None => {
             let input = io::stdin().lock();
             let output = io::stdout().lock();
             uci::uci_loop(input, output).unwrap_or_else(|e| println!("{e}"));