style: expand section spacing and page top/bottom margins across all pages

refer_landing_page/app/lectures/page.tsx

@@ -6,7 +6,7 @@ export default function LecturesPage() {
   const olderSemesters = semesters.slice(3);
 
   return (
-    <div className="container-content space-y-16 py-6">
+    <div className="container-content space-y-20 md:space-y-28 py-10 md:py-16">
       {/* Header */}
       <section className="space-y-3">
         <div className="flex items-center gap-3">
@@ -24,7 +24,7 @@ export default function LecturesPage() {
       </section>
 
       {/* Recent 3 Semesters */}
-      <section className="space-y-6 pt-6 border-t border-line">
+      <section className="space-y-6 pt-12 md:pt-16 border-t border-line">
         <div className="flex justify-between items-end">
           <div>
             <div className="font-mono text-xs text-vermillion uppercase tracking-widest font-bold">