fix(storybook): refine responsive page inner width

- Story page Inner side margin: 16px up to a 480px viewport, linear to 60px at 768px, 60px beyond (no width jump)
- Follow the 60px margins: Responsive 1920 row from a 2040px page (was 2000px); property compare 3 columns from 1125px, 2 columns from 787px (was 1080 / 720)
- SW browser tests: drop the removed --sb-page-max-width override, compare thresholds 787 / 1125

src/components/story-page.css

@@ -1,5 +1,5 @@
 /* Storybook presentation only. Common page frame for representative Stories; all selectors stay inside .sb-page.
-   Inner (fluid, 60px each side; vertical gutter 16–40) and title (kicker 12 / title 28·36·700 / description, underlined) reuse Foundation / Color.
+   Inner (fluid; 16px each side up to 480px, growing to 60px at 768px; vertical gutter 16–40) and title (kicker 12 / title 28·36·700 / description, underlined) reuse Foundation / Color.
    Section reuses the Center Graphic / 교량 split: heading + description, a divider, then the specimen. */
 .sb-page {
   --sb-page-gutter: clamp(16px, 3vw, 40px);
@@ -12,8 +12,10 @@
 }
 .sb-page > .sb-page-inner {
   box-sizing: border-box;
-  /* 2026-11-05 (user request): no max width; the Inner follows the page width and keeps 60px on each side. */
-  width: calc(100% - 120px);
+  /* 2026-11-05 (user request): no max width; the Inner follows the page width. Side margin (each side) = 16px up to a
+     480px viewport (358px Inner at 390px, so a 314px specimen fits), then linear to 60px at 768px (44px over 288px,
+     11 / 72 of the viewport growth), 60px from 768px. The Inner keeps growing (about 0.69px per 1px), with no jump. */
+  width: calc(100% - 2 * clamp(16px, calc(16px + (100vw - 480px) * 11 / 72), 60px));
   min-width: 0;
   margin-inline: auto;
 }