UNO polish: center nav-rail items, drop per-page XP bar, shop category tabs

- NavRail: vertically center items in the side rail (was top-aligned).
- ScreenHeader: showXp defaults off — the level/XP bar no longer clutters every
  sub-page (it lives on Home's chip + the Profile page).
- Shop: category tabs (avatars / fronts / backs / reactions / stickers / titles
  / XP) so only one category shows at a time — no more endless scroll.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/online/NavRail.tsx

@@ -39,7 +39,7 @@ export function NavRail({ bottom = false }: { bottom?: boolean }) {
           : cn(
               // portrait: bottom bar; landscape: side rail
               "border-t border-gold/10 pb-[max(0.375rem,env(safe-area-inset-bottom))]",
-              "landscape:order-first landscape:h-full landscape:w-[78px] landscape:flex-col landscape:justify-start",
+              "landscape:order-first landscape:h-full landscape:w-[78px] landscape:flex-col landscape:justify-center",
               "landscape:gap-1.5 landscape:py-3 landscape:pb-3 landscape:border-t-0",
               "ltr:landscape:border-r rtl:landscape:border-l"
             )

src/components/online/ScreenHeader.tsx

@@ -10,12 +10,12 @@ export function ScreenHeader({
   title,
   back = "home",
   right,
-  showXp = true,
+  showXp = false,
 }: {
   title: string;
   back?: Screen;
   right?: React.ReactNode;
-  /** Show the persistent level + XP chip beneath the header (default on). */
+  /** Show the persistent level + XP chip beneath the header (default off). */
   showXp?: boolean;
 }) {
   const navBack = useUIStore((s) => s.back);

src/components/screens/ShopScreen.tsx

@@ -78,6 +78,7 @@ export function ShopScreen() {
   const [items, setItems] = useState<ShopItem[]>([]);
   const [msg, setMsg] = useState("");
   const [detail, setDetail] = useState<ShopItem | null>(null);
+  const [cat, setCat] = useState<ShopItem["kind"]>("avatar");
 
   useEffect(() => {
     getService().getShopItems().then(setItems);
@@ -187,16 +188,37 @@ export function ShopScreen() {
         </div>
       )}
 
-      {sections.map((sec) => {
+      {/* category tabs */}
+      <div className="flex gap-2 overflow-x-auto pb-2 -mx-1 px-1 mb-3">
+        {sections.map((sec) => (
+          <button
+            key={sec.kind}
+            onClick={() => setCat(sec.kind)}
+            className={cn(
+              "shrink-0 rounded-full px-4 py-2 text-sm font-bold transition whitespace-nowrap",
+              cat === sec.kind ? "btn-gold" : "panel text-cream/70 hover:text-cream"
+            )}
+          >
+            {sec.title}
+          </button>
+        ))}
+      </div>
+
+      {sections
+        .filter((sec) => sec.kind === cat)
+        .map((sec) => {
           const list = items.filter((i) => i.kind === sec.kind);
-        if (!list.length) return null;
           return (
             <Section key={sec.kind} title={sec.title} hint={sec.hint}>
+              {list.length === 0 ? (
+                <p className="text-center text-cream/40 text-sm py-8">{t("shop.emptyCat")}</p>
+              ) : (
                 <div className="grid grid-cols-3 sm:grid-cols-4 lg:grid-cols-6 gap-3">
                   {list.map((item) => (
                     <ItemCard key={item.id} item={item} owned={owns(item)} reqLabel={lockLabel(item)} onOpen={() => setDetail(item)} />
                   ))}
                 </div>
+              )}
             </Section>
           );
         })}

src/lib/i18n.tsx

@@ -320,6 +320,7 @@ const fa: Dict = {
   "shop.reqLevel": "سطح",
   "shop.reqRating": "امتیاز",
   "shop.reqAchv": "دستاورد:",
+  "shop.emptyCat": "آیتمی در این دسته نیست",
   "reward.newTitle": "عنوان جدید",
 
   "reactions.title": "شکلک",
@@ -666,6 +667,7 @@ const en: Dict = {
   "shop.reqLevel": "Level",
   "shop.reqRating": "Rating",
   "shop.reqAchv": "Achievement:",
+  "shop.emptyCat": "No items in this category",
   "reward.newTitle": "New title",
 
   "reactions.title": "Emoji",