* fix(website): expand Founder Portal layout width to fill available canvas
* fix(website): restore mobile padding, preserve public main landmark, and harden width test
Apply responsive mobile padding to .site-page-frame under 760px. Render semantic <main> for public routes and <div> for portal routes with internal <main> via SitePageFrame. Assert max-w-[1536px] exclusively and reject old max-w-[1440px] cap in founder-portal.test.cjs.
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Co-authored-by: Developer <dev@example.com>
