user-app: redesigned home screen and product detail

Design language introduced here and reused across both screens:
  - LESS colour tokens (@ink/@inkSoft/@inkMuted/@inkFaint, @wine/@wineSoft,
    @canvas/@canvasSoft, @hairline/@hairlineSoft) added to
    themeConfig/colors.json and injected globally via vite's modifyVars, so
    scoped <style lang="less"> blocks resolve them with no import
  - BEM-ish scoped class names, hairline-bordered cards at 14-18px radii,
    ink surfaces with a wine accent, dashed-border empty states
  - components/home/: SectionHead, ShowcaseCard, ShowcaseSlider, CategoryRail,
    RateStrip, AccountStrip

Data honesty is deliberate throughout: no rial price is printed for a piece,
because a finished item's price is the live gold rate x weight plus wage,
computed at order time and never stored on the product. Only genuinely
present fields are shown (weight, making-charge percent, stock, category,
brand). Categories and the hero are derived from the real catalogue, so an
empty catalogue renders an empty state rather than placeholder tiles.

Also fixes a real bug in the product detail view: it ran, at module scope,
history.pushState + window.onpopstate = () => history.go(1). Because the
drawer mounts its slot eagerly, that fired for every product card on the
home screen and permanently hijacked the back button for the session.

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

apps/user-app/src/api/client.ts

@@ -19,6 +19,12 @@ export interface ProductVariantSummary {
   title: string;
   rashWeightGrams: string;
   defaultWagePercent: string;
+  /// On-hand stock and the "orderable at zero stock" flag. Both exist on
+  /// ProductVariant and are already returned by GET /catalog/products (the
+  /// catalog service includes every variant field) — declared here so the UI
+  /// can read them.
+  qty?: number;
+  isPreOrder?: boolean;
 }
 
 export interface CategorySummary {
@@ -43,6 +49,9 @@ export interface ProductSummary {
   id: string;
   title: string;
   description: string | null;
+  /// Legacy Product.product_code — the human-facing code. Already returned by
+  /// GET /catalog/products.
+  productCode?: string | null;
   variants: ProductVariantSummary[];
   images: Array<{ url: string }>;
   category: CategorySummary | null;