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/subscription/Subscription.css

@@ -1139,19 +1139,16 @@
 
 /* ── 반응형 ───────────────────────────────────────────────────────────── */
 
-@media (max-width: 1100px) {
+@media (max-width: 1024px) {
     .sub-list-layout { grid-template-columns: 1fr 360px; }
 }
 
-@media (max-width: 900px) {
+@media (max-width: 768px) {
     .sub-list-layout { grid-template-columns: 1fr; }
     .sub-detail-panel { position: static; }
     .sub-profile-card { grid-template-columns: 1fr; }
     .sub-profile-card__right { flex-direction: column; align-items: flex-start; }
     .sub-profile-score__breakdown { min-width: 0; width: 100%; }
-}
-
-@media (max-width: 768px) {
     .sub-header { grid-template-columns: 1fr; }
     .sub-stats-bar { display: grid; grid-template-columns: repeat(2, 1fr); }
     .sub-stat-item { border-right: none; border-bottom: 1px solid var(--line); }