fix: persist UI preferences across navigation and sessions (#48)

## Summary

- **#35** — Adventure multiplier selection is now persisted in `localStorage` (`"elysium_batch_size"`). The chosen batch size is restored automatically on the next visit, with a graceful fallback to `1` for missing or unrecognisable values.
- **#36** — Zone selection in the boss panel and quest panel is now persisted in `sessionStorage` (`"elysium_boss_zone"` / `"elysium_quest_zone"`). The selected zone survives navigation within a session and resets cleanly when the session ends, defaulting to Verdant Vale if no stored value exists.

## Test plan

- [x] Lint — zero errors, zero warnings
- [x] Build — all packages build cleanly
- [x] Tests — 415 tests passing, 100% coverage across all packages
- [ ] Manual: select a non-default batch size, refresh the page — multiplier should be restored
- [ ] Manual: switch to a non-default zone in the boss panel, navigate away and back — zone should still be selected
- [ ] Manual: repeat for the quest panel
- [ ] Manual: log out and back in — zone selection should reset to Verdant Vale

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #48
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

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

@@ -108,9 +108,9 @@ const QuestCard = ({
           </p>
         }
         <div className="quest-rewards">
-          {quest.rewards.map((reward) => {
+          {quest.rewards.map((reward, rewardIndex) => {
             return (
-              <span className="reward-tag" key={`${reward.type}-${String(reward.amount ?? "")}`}>
+              <span className="reward-tag" key={`${reward.type}-${reward.targetId ?? String(reward.amount ?? rewardIndex)}`}>
                 {reward.type === "gold"
                   && `🪙 ${formatNumber(reward.amount ?? 0)}`}
                 {reward.type === "essence"
@@ -184,7 +184,9 @@ const QuestCard = ({
  */
 const QuestPanel = (): JSX.Element => {
   const { state, toggleAutoQuest } = useGame();
-  const [ activeZoneId, setActiveZoneId ] = useState("verdant_vale");
+  const [ activeZoneId, setActiveZoneId ] = useState(() => {
+    return sessionStorage.getItem("elysium_quest_zone") ?? "verdant_vale";
+  });
   const [ showLocked, setShowLocked ] = useState(true);
 
   if (state === null) {
@@ -243,6 +245,11 @@ const QuestPanel = (): JSX.Element => {
     }
   }
 
+  function handleZoneSelect(zoneId: string): void {
+    setActiveZoneId(zoneId);
+    sessionStorage.setItem("elysium_quest_zone", zoneId);
+  }
+
   function handleToggle(): void {
     setShowLocked((current) => {
       return !current;
@@ -285,7 +292,7 @@ const QuestPanel = (): JSX.Element => {
 
       <ZoneSelector
         activeZoneId={activeZoneId}
-        onSelectZone={setActiveZoneId}
+        onSelectZone={handleZoneSelect}
         zones={zones}
       />