fix: prevent horizontal wobble on mobile scroll

- Replace overflow-x:hidden with overflow-x:clip on html/body/.obp-main/.VPPageContent
  (clip does not create a scroll container so position:fixed nav is unaffected)
- Fix grid minmax to use min(300px,100%) so cards never overflow narrow viewports
- Books row keeps overflow-x:auto for intentional horizontal scroll

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

Author: nash-efp

.vitepress/theme/style.css

@@ -39,12 +39,9 @@
 }/* ===== Reset / Base ===== */
 * { box-sizing: border-box; }
 
-html {
-  overflow-x: hidden;
-}
-
-body {
-  overflow-x: hidden;
+html, body {
+  overflow-x: clip; /* clipはスクロールコンテナを生成しないため position:fixed に影響しない */
+  max-width: 100%;
   background: var(--color-bg) !important;
   font-family: 'Inter', 'Noto Sans JP', system-ui, -apple-system, sans-serif !important;
 }
@@ -82,8 +79,8 @@ body {
 
 .VPPageContent {
   padding: 0 !important;
-  overflow-x: hidden;
-  max-width: 100vw;
+  overflow-x: clip;
+  max-width: 100%;
 }
 
 /* ===== Hero Section ===== */
@@ -393,6 +390,7 @@ body {
   max-width: 1120px;
   margin: 0 auto;
   padding: 0 2rem 6rem;
+  overflow-x: clip; /* 書籍行のスクロールコンテナは内部で動作し続ける */
 }
 
 /* ===== Section ===== */
@@ -503,7 +501,7 @@ body {
 /* ===== Card Grid ===== */
 .obp-grid {
   display: grid;
-  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
+  grid-template-columns: repeat(auto-fill, minmax(min(300px, 100%), 1fr));
   gap: 16px;
 }