Check existing days faster

resources/loader.js

@@ -14,7 +14,7 @@ async function getDayList() {
   const days = []
 
   for (let i = 1; i <= 25; i++) {
-    const response = await fetch(`/days/${i}/code.wat`)
+    const response = await fetch(`/days/${i}/code.wat`, { method: 'head' })
 
     if (response.status === 200) {
       days.push(i)