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/themeConfig/colors.json

@@ -22,5 +22,17 @@
   "gray-400": "#9ca3af",
   "gray-500": "#6b7280",
   "green": "#16a34a",
-  "red": "#dc2626"
+  "red": "#dc2626",
+  "ink": "#14161A",
+  "inkSoft": "#22262E",
+  "inkMuted": "#5B616E",
+  "inkFaint": "#8A909C",
+  "wine": "#7A1B33",
+  "wineDeep": "#5E1427",
+  "wineSoft": "#A33C55",
+  "wineWash": "#FBF2F4",
+  "canvas": "#FFFFFF",
+  "canvasSoft": "#FAFAFA",
+  "hairline": "#ECEDEF",
+  "hairlineSoft": "#F4F5F6"
 }