fix(nav): soft-nav cross-route mobile drawer links instead of a full reload #272

Summary

The mobile drawer still forces a full page reload when one of its section links is tapped from another route (e.g. /blog/*, /legal/*). MobileMenu.tsx:177 calls window.location.assign(isHome ? "/" : /#${anchor}) in the drawer's close cleanup.

That reload was a workaround for the Next 16 App Router hash-appending bug (#116). Next 16.3.8 fixes that bug, and #270 already removes the matching workaround from the desktop nav (Chrome.tsx). The drawer should behave the same way, so it doesn't do a full page reload when the site can navigate without one.

Evidence (from #270)

The test drove headless Chrome against the static export:

• router.push('/#method') after a reload gives /#method#method on Next 16.2.6 and a clean /#method on 16.3.8.
• Going to a section from another page with router.push('/#id') lands on the same URL and the same scroll position as location.assign.

Proposed change

• In the drawer's close cleanup, replace window.location.assign(...) with router.push(...) from next/navigation. Keep it after the body unlock, so the pinned position: fixed body is released before the navigation.
• Update the comment that calls the soft-nav path unreliable.

Acceptance

• From /blog/, a blog post and /legal/privacy/ at mobile width, tapping each drawer section navigates without a reload, lands on the section with a single clean hash, and leaves the body unpinned.
• Tapping home from another route lands on / with no hash.
• Same-page drawer taps are unchanged.

Depends on #270 (the Next 16.3.8 bump).