Add customer auth, real cart/checkout, store-items pages, comments, contact form

- Real in-site login/register (password + SMS OTP) against Meshkee's
  /auth API, with self-healing access-token refresh (15 min lifetime) and
  an in-flight-refresh guard so AuthContext and CartContext don't race
  each other into a failed concurrent refresh.
- Real cart: header cart button/badge, a cart popup, and a working
  "add to cart" on both product cards (where a specific variant id is
  known) and the product/store-item detail buy-box (always resolves a
  purchasable variant, even for single-SKU products with no selectable
  variation).
- /checkout: address + cash/bank-transfer payment, posts to the real
  checkout API and creates an order; refreshes the cart afterward so the
  header badge doesn't go stale.
- New /store-items and /store-items/[id] pages (variant-level browsing,
  separate from the product-level /products catalog), cross-referencing
  the parent product for images/description/technical-info.
- Product gallery: click-to-open fullscreen lightbox alongside the
  existing hover-zoom.
- Comments tab wired to the real comments API, gated to logged-in users
  (a product decision — the API itself doesn't require auth) with a
  login prompt otherwise.
- Similar-products row on product/store-item detail pages.
- Contact page wired to the real contact-submissions API, with a toast
  and inline confirmation on success, and the form resetting.
- CONTEXT.md: a maintained architecture/conventions doc for this repo,
  now auto-loaded via CLAUDE.md, covering the Meshkee integration quirks
  and UI conventions established across this project.

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

src/app/layout.tsx

@@ -5,6 +5,7 @@ import "./globals.css";
 import { TopBar } from "@/components/home/TopBar";
 import { Header } from "@/components/home/Header";
 import { Footer } from "@/components/home/Footer";
+import { Providers } from "@/context/Providers";
 import { getBusinessInfo, getCategories, getCategoryTree } from "@/lib/meshkee";
 
 // Body text — headings use the bold weight instead, see globals.css.
@@ -45,10 +46,12 @@ export default async function RootLayout({ children }: LayoutProps<"/">) {
       className={`${iranyekan.variable} ${iranyekanBold.variable} ${syne.variable} h-full antialiased`}
     >
       <body className="min-h-full flex flex-col">
-        <TopBar />
-        <Header categoryTree={categoryTree} categories={categories} />
-        <main>{children}</main>
-        <Footer businessInfo={businessInfo} categories={categories} />
+        <Providers businessId={businessInfo?.id ?? "1"}>
+          <TopBar />
+          <Header categoryTree={categoryTree} categories={categories} />
+          <main>{children}</main>
+          <Footer businessInfo={businessInfo} categories={categories} />
+        </Providers>
       </body>
     </html>
   );