fix: proper RTL desktop layout — center content, fix nav offset

Changed lg:mr to lg:pr for nav clearance (RTL-correct), centered
content container at 720px max-width, aligned header to same width.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/layout/AppShell.tsx

@@ -7,12 +7,12 @@ import { usePresence } from '../../hooks/usePresence';
 export function AppShell() {
   usePresence();
   return (
-    <div className="flex min-h-dvh">
+    <div className="min-h-dvh">
       <DesktopNav />
-      <div className="flex-1 flex flex-col min-h-dvh lg:mr-[72px]">
+      <div className="flex flex-col min-h-dvh lg:pr-[72px]">
         <Header />
-        <main className="flex-1 pb-[calc(var(--bottom-nav-height)+env(safe-area-inset-bottom))] lg:pb-0">
-          <div className="w-full max-w-[800px] mx-auto lg:px-6">
+        <main className="flex-1 pb-[calc(var(--bottom-nav-height)+env(safe-area-inset-bottom))] lg:pb-6">
+          <div className="w-full max-w-[720px] mx-auto">
             <Outlet />
           </div>
         </main>

src/components/layout/Header.tsx

@@ -9,9 +9,9 @@ interface HeaderProps {
 
 export function Header({ coins = 0, gems = 0, level = 1, unreadCount = 0 }: HeaderProps) {
   return (
-    <header className="sticky top-0 z-40 bg-bg-1/95 backdrop-blur-sm border-b border-white/6"
+    <header className="sticky top-0 z-40 bg-bg-1/95 backdrop-blur-sm border-b border-white/6 lg:pr-[72px]"
       style={{ paddingTop: 'env(safe-area-inset-top)' }}>
-      <div className="flex items-center justify-between h-[var(--header-height)] px-5">
+      <div className="flex items-center justify-between h-[var(--header-height)] px-5 max-w-[720px] mx-auto">
         <div className="flex items-center gap-3">
           <Link to="/" className="text-gold font-bold text-lg font-latin tracking-tight">
             EL3AB