feat: persist zone selection across panel navigation in sessionStorage

Both the boss panel and the quest panel now read their active zone from
sessionStorage on mount and write back to it whenever the user selects
a new zone. The stored selections are cleared automatically when the
session ends, and fall back to verdant_vale when no stored value exists.

Closes #36

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

@@ -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}
       />