Why

Feedback from Jenny: on mobile it's difficult or impossible to switch frameworks without going back to the homepage. We deep-link to framework-level pages from the corp site and ~50% of that traffic is mobile.

The only existing path was the easy-to-miss ← Back to main menu link in the hamburger, behind an entry labeled SDKs (nothing says "framework"), and its links dropped users on the Installation page instead of keeping the page they were reading.

What

Phones (<768px) — an in-page framework + version selector, styled like the homepage one, at the top of every doc page (above "On this page"):

• Switching framework keeps the current page and version (e.g. /sdks/android/id-capture/intro → /sdks/ios/id-capture/intro); pages that don't exist in the target framework fall back via the existing NotFound redirect, same as desktop today.
• Version pill mirrors the navbar version dropdown: Stable/Legacy tags, keeps the current page, offers only 7.6.14/6.28.10 on Xamarin pages.
• Breadcrumbs and the "Back to main menu" button are hidden on mobile (the sidebar already highlights the open page), and the content top padding is reduced 48px → 16px.

Tablets (768–996px) — the existing navbar version/framework dropdowns are shown next to the search (they were CSS-hidden below 997px); the in-page selector is hidden in this range. Dropdowns open on tap.

Desktop (≥997px) — unchanged.

Also:

• Extracted the desktop dropdown's path-preserving link logic into a shared useFrameworkItems hook (the DropdownNavbarItem override shrinks by ~190 lines, identical behavior). The mobile SDKs dropdown entries now also keep the current page.
• Fixed the homepage framework selector dropdown being painted over by the SkillsCallout (equal z-index, later DOM order — panel raised to z-index 20).
• src/theme/DocItem/Layout is a faithful copy of the stock component with one added line (selector above the mobile TOC).

Notes for reviewers

• ⚠️ Hiding "Back to main menu" means Log In / Sign Up are no longer reachable on mobile doc pages (they only lived in the hamburger primary menu). One-line CSS revert in navbar-sidebar.scss if we want them back.
• Framework links are computed after hydration (same as before this PR) so the broken-link checker stays green for pages that don't exist in every framework.

Testing

• yarn typecheck and yarn build pass.
• Playwright-verified on iPhone 13 viewport, 768px and 915px tablet widths, and 1440px desktop: switching frameworks/versions navigates correctly and preserves the page, Xamarin filtering works on legacy versions, no console errors.