fix(main): keep prefs.mode in sync and rAF-coalesce mutation observer

src/main.js

@@ -27,6 +27,7 @@ function start() {
     },
     onModeChange: (m) => {
       store.setMode(m);
+      prefs.mode = m;
       applyMode();
     },
     onPosChange: (pos) => store.setPos(pos),
@@ -85,10 +86,16 @@ function start() {
   render();
 
   // watch DOM for attribute changes
+  let pending = false;
   const observer = new MutationObserver(() => {
+    if (pending) return;
+    pending = true;
+    requestAnimationFrame(() => {
+      pending = false;
       const a = currentAttribute();
       if (a && (a.attr !== lastAttr || a.current !== lastSnapshot?.current)) render();
     });
+  });
   observer.observe(document.body, { childList: true, subtree: true, characterData: true });
 
   // intercept train requests