Wrap mode_toggle.js as arrow function to match Gradio js= convention

static/mode_toggle.js

@@ -1,3 +1,4 @@
+() => {
 window.__selectedMode = 'fast';
 window.__setMode = function(m) {
     window.__selectedMode = m;
@@ -6,3 +7,4 @@ window.__setMode = function(m) {
     if (fast) fast.classList.toggle('mode-btn-active', m === 'fast');
     if (hd)   hd.classList.toggle('mode-btn-active',   m === 'high_detail');
 };
+}