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

packages/sw/tests/theme-inheritance.browser.mjs

@@ -39,7 +39,6 @@ const newPage = async (width = 1440, height = 1000) => {
 const open = async (page, id) => {
   await page.goto(`${storybook}/iframe.html?id=${id}&viewMode=story`)
   await page.waitForSelector('#storybook-root > *')
-  await page.addStyleTag({ content: '.sb-page { --sb-page-max-width: 100vw; }' })
   await page.evaluate(() => document.fonts.ready)
   await page.waitForTimeout(300)
 }