feat: Arrow keys to move back in the current line

src/routes/+page.svelte

@@ -669,6 +669,7 @@
     }
     selected = null;
     highlights = [];
+    playSound('undo');
   }
 
   function resetBoard(showSelection = true) {
@@ -1354,8 +1355,21 @@
     }
     moveTags[currentRep] = { ...moveTags[currentRep] };
   }
+
+  function handleKeyDown(e) {
+    if (e.key === 'ArrowLeft') {
+      const target = e.target;
+      if (target && (target.tagName === 'INPUT' || target.tagName === 'TEXTAREA' || target.isContentEditable)) {
+        return;
+      }
+      e.preventDefault();
+      goBack();
+    }
+  }
 </script>
 
+<svelte:window onkeydown={handleKeyDown} />
+
 <svelte:head>
   <title>Chess Opening Repertoire Builder</title>
 </svelte:head>