Re-wire MobileMenu into Chrome.tsx on top of main's nav #87

Context

PR #56 (feat/mobile-menu-drawer) was developed before the /blog routes landed on main. When merging main back into the branch in commit ae1fcc3, the Chrome.tsx integration was parked: Chrome.tsx was reset to main's version verbatim and lib/sections.ts was deleted. The drawer's other pieces still ship in the PR:

• components/site/MobileMenu.tsx (compiles standalone with inlined section constants)
• The .mm-toggle / overlay / panel block in app/globals.css
• The --mm-i augmentation in types/css.d.ts

…but they're unreferenced. The mobile menu does not render until Chrome.tsx is re-wired.

The rollback was the right call short-term — main's Chrome.tsx had picked up next/link, /#section anchors (required so the navbar works from /blog/* routes), and a new Blog link, all of which would have made hand-stitching a hybrid risky. Easier to re-do the integration cleanly on top of main than to defend the merge resolution in review.

What needs to happen

1. Re-import and render MobileMenu inside Chrome.tsx, after the Litepaper link in the right cluster.
2. Add mobileOpen state + a handleMobileOpenChange callback (useCallback) passed in as onOpenChange.
3. Compute toggleTone: mobileOpen ? \"paper\" : onDark ? \"ink\" : \"paper\". Pass as the tone prop.
4. Hide desktop links on phones: add hidden ... md:flex to the Docs / Blog / Litepaper links so the drawer toggle replaces them <md. Don't break the border-b border-current pb-[2px] migration on Docs/Blog.
5. Add Blog to MobileMenu.tsx's EXTERNAL list (between Docs and Litepaper, external: false) so the drawer matches the desktop nav.
6. Decide on lib/sections.ts — if Chrome and MobileMenu both want the same SECTION_IDS / NAV_SECTIONS / DARK_SECTIONS, re-extract; otherwise leave inline in both.

Pointers

• Last working integration: commit c240b60 (pre-merge HEAD of this branch).
• Verbatim main baseline: commit ae1fcc3 (the merge commit).
• Diff that needs reapplying lives in c240b60..ae1fcc3^1 -- components/site/Chrome.tsx lib/sections.ts.

Verification

• pnpm lint && pnpm test && pnpm build must pass.
• Manual smoke at /, / on a <md viewport, /blog/, /blog/<slug> — see the verification block in the original plan.

Tracked from PR #56.