feat: add auto-prestige toggle via runestone shop upgrade

Adds a new Utility category to the prestige shop with the "Autonomous Ascension" upgrade (100 runestones). Once purchased, a toggle button appears in the shop that enables automatic prestige — the client RAF loop checks the threshold on each tick and fires the prestige API automatically using the current character name.

✨ This feature was implemented with help from Hikari~ 🌸

apps/web/src/components/game/PrestigePanel.tsx

@@ -36,10 +36,11 @@ const CATEGORY_ORDER: PrestigeUpgradeCategory[] = [
   "essence",
   "crystals",
   "runestones",
+  "utility",
 ];
 
 export const PrestigePanel = (): React.JSX.Element => {
-  const { state, reload, formatNumber, buyPrestigeUpgrade } = useGame();
+  const { state, reload, formatNumber, buyPrestigeUpgrade, toggleAutoPrestige } = useGame();
   const [characterName, setCharacterName] = useState("");
   const [isPending, setIsPending] = useState(false);
   const [result, setResult] = useState<{ runestones: number; count: number; milestoneRunestones: number } | null>(null);
@@ -205,6 +206,9 @@ export const PrestigePanel = (): React.JSX.Element => {
                   const canAfford = prestigeData.runestones >= upgrade.runestonesCost;
                   const isLoading = buyingId === upgrade.id;
 
+                  const isAutoPrestigeToggle = upgrade.id === "auto_prestige" && purchased;
+                  const autoPrestigeEnabled = prestigeData.autoPrestigeEnabled ?? false;
+
                   return (
                     <div
                       key={upgrade.id}
@@ -217,6 +221,15 @@ export const PrestigePanel = (): React.JSX.Element => {
                           {purchased ? "✅ Purchased" : `🔮 ${formatNumber(upgrade.runestonesCost)} Runestones`}
                         </p>
                       </div>
+                      {isAutoPrestigeToggle && (
+                        <button
+                          className={`auto-prestige-toggle ${autoPrestigeEnabled ? "enabled" : "disabled"}`}
+                          onClick={() => { toggleAutoPrestige(); }}
+                          type="button"
+                        >
+                          {autoPrestigeEnabled ? "⚡ Auto ON" : "⏸ Auto OFF"}
+                        </button>
+                      )}
                       {!purchased && (
                         <button
                           className="buy-upgrade-button"