show board dates in UTC on the website

Board days are UTC epoch days (midnight UTC), but toLocaleDateString
formatted them in the viewer's timezone, so anyone west of UTC saw
every game dated the day before. Format them in UTC.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

www/html/wordle/game.html

@@ -316,8 +316,11 @@ async function loadBoard() {
 
     // If we know the exact epoch day and haven't set date text yet, show it
     if (finalEpoch !== null && !dateEl.textContent) {
+        // Epoch days start at midnight UTC, so format in UTC or viewers
+        // west of UTC see the previous day
         dateEl.textContent = new Date(finalEpoch * 86400 * 1000)
             .toLocaleDateString(undefined, {
+                timeZone: "UTC",
                 weekday: "long",
                 year: "numeric",
                 month: "long",

www/html/wordle/games.html

@@ -134,8 +134,11 @@
 
 <script>
 function formatDateFromEpochDays(epochDays) {
+  // Epoch days start at midnight UTC, so format in UTC or viewers
+  // west of UTC see the previous day
   const date = new Date(epochDays * 86400 * 1000);
   return date.toLocaleDateString(undefined, {
+    timeZone: "UTC",
     weekday: "short",
     year: "numeric",
     month: "short",