style: add vertical padding above and below AppHeader for generous layout spacing

refer_landing_page/components/Header.tsx

@@ -26,9 +26,9 @@ export default function Header() {
       : false;
 
   return (
-    <header className="sticky top-0 z-50 border-b border-ink bg-ivory/85 backdrop-blur">
+    <header className="sticky top-0 z-50 border-b border-ink bg-ivory/85 backdrop-blur py-2 sm:py-3">
       {/* Journal issue strip — magazine masthead feel. */}
-      <div className="hidden border-b border-line desktop:block">
+      <div className="hidden border-b border-line pb-2 mb-2 desktop:block">
         <div className="container-content flex items-center justify-between py-1.5">
           <span className="kicker">Issue 01 — 2026</span>
           {/* CUSTOMIZATION HOOK: masthead tagline */}
@@ -39,7 +39,7 @@ export default function Header() {
         </div>
       </div>
 
-      <div className="container-content flex h-[4.25rem] items-center justify-between gap-8">
+      <div className="container-content flex min-h-[4.5rem] items-center justify-between gap-8 py-2 sm:py-3">
         {/* Brand logo — explicit right margin to guarantee clear separation from 01 HOME */}
         <Link
           href="/"