Move the completed change to
openspec/changes/archive/2026-09-17-pin-home-category-menu/ and merge its
delta into openspec/specs/frontend-mall/spec.md.
Modified requirements:
- B2B2C mall-style PC storefront shell: the header stays fully visible
while scrolling (no scroll-based auto-hide), and the category mega-menu
is a hover dropdown on every page except home, where it is pinned in
the hero row. Adds the "header persists while scrolling" and "hover
categories on a non-home page" scenarios.
- Mock PC home page: the hero row is a pinned 240px category sidebar plus
a carousel filling the remainder, both 450px tall, with the mega-menu
overlaying the carousel and banners center-cropped. Adds the "sidebar
stays while scrolling" and "expand a category" scenarios.