user-app: extend the redesign across the purchase path

Applies the home/product-detail design language (LESS colour tokens, BEM
class names, hairline-bordered cards, SectionHead, dashed empty states) to
the screens a shopper actually walks through: search, collection, newest,
cart and favorites.

Two shared pieces are extracted so the language stays consistent rather than
re-typed per screen:
  - components/ui/PageBar.vue — the sticky translucent bar with blur and a
    hairline, lifted from the home screen's own header so every other screen
    gets identical chrome instead of the old dark AppHeader.
  - components/product/ProductCard.vue — the catalogue workhorse card. It is
    deliberately a sibling of home/ShowcaseCard (which keeps its editorial "wide"
    variant and badge) and additionally surfaces stock, which the
    catalogue needs and the home screen does not.

Deleted as orphaned once nothing imported them: ProductList,
ProductVerticalFull, ProductVertical, ProductHorizontal, CollectionCard —
all Tailwind utility soup carried over from the legacy PWA.

Behaviour is preserved throughout; only chrome and cards change. The cart
still posts to the real POST /orders with wagePercent from each item's
pinned variant, still gates on a real session, and still keeps the note
drawer and success step. Search keeps its client-side filtering, the Filters
sheet, category chips and collection tiles. No rial price is printed
anywhere, for the same reason as the rest of the redesign: a finished
piece's price is the live gold rate x weight plus wage, computed at order
time and never stored on the product.

FIXED a regression this redesign introduced before it shipped: dropping
ScrollFetchSearch from the search grid meant all 205 catalogue products
mounted at once (205 cards, 205 images). Both search and newest now render
a 20-item window that grows as the user reaches the end.

Verified in a real browser against the running API and native database, not
just a green build: home 13 cards, search 20 -> 40 -> 60 -> 80 on scroll,
newest 20 -> 40 -> 60, cart empty state, favorites 3 cards behind a seeded
session. All images loaded (0 broken), no horizontal overflow, no console
errors beyond pre-existing vue3-lazyload noise that predates this work.
vue-tsc and vite build both clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/user-app/src/composables/useProduct.ts

@@ -1,7 +1,9 @@
 // Adapts our actual ProductSummary (apps/user-app/src/api/client.ts) into the
-// same output shape legacy's Mixins/product/index.ts `useProduct()` produced,
-// so the ported product-card components (ProductHorizontal/ProductVertical/
-// ProductVerticalFull) can render unchanged.
+// same output shape legacy's Mixins/product/index.ts `useProduct()` produced.
+// The legacy card components it was originally shaped for (ProductHorizontal/
+// ProductVertical/ProductVerticalFull) are gone, replaced by the redesigned
+// components/product/ProductCard.vue, components/home/ShowcaseCard.vue and
+// components/product/CartItem.vue — all of which consume this same contract.
 //
 // Honest gaps vs. legacy (no backend equivalent exists yet — apps/api was not
 // touched to add these):