style(responsive): standardize Subscription, MusicStudio, BlogMarketing breakpoints

- Subscription.css: 1100px → 1024px; merge 900px into 768px block
- MusicStudio.css: 960px → 1024px; both 640px blocks → 480px
- BlogMarketing.css: 640px → 480px

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/pages/music/MusicStudio.css

@@ -317,7 +317,7 @@
     align-items: start;
 }
 
-@media (max-width: 960px) {
+@media (max-width: 1024px) {
     .ms-layout {
         grid-template-columns: 1fr;
     }
@@ -487,7 +487,7 @@
     gap: 8px;
 }
 
-@media (max-width: 640px) {
+@media (max-width: 480px) {
     .ms-genre-grid {
         grid-template-columns: repeat(2, 1fr);
     }
@@ -1696,7 +1696,7 @@
 /* ═══════════════════════════════════════════════════
    MOBILE
 ═══════════════════════════════════════════════════ */
-@media (max-width: 640px) {
+@media (max-width: 480px) {
     .ms-header__title {
         font-size: clamp(44px, 14vw, 70px);
     }