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/components/home/Header.tsx

@@ -4,13 +4,15 @@ import { useEffect, useRef, useState } from "react";
 import { createPortal } from "react-dom";
 import type { Category, CategoryNode, CategoryTreeGroup } from "@/lib/meshkee";
 import { EmptyState } from "@/components/ui/EmptyState";
+import { CartButton } from "@/components/cart/CartButton";
 import { SearchBar } from "./SearchBar";
 
 const navLinks = [
+  { label: "فروشگاه", href: "/store-items" },
   { label: "فروش ویژه", href: "#" },
   { label: "درباره ما", href: "#" },
   { label: "سوالات متداول", href: "#" },
-  { label: "تماس با ما", href: "#" },
+  { label: "تماس با ما", href: "/contact" },
 ];
 
 const LOGIN_URL = "https://customer.sanihome.ir";
@@ -251,16 +253,7 @@ export function Header({
               <span>👤</span>
               <span>ورود</span>
             </a>
-            <button
-              type="button"
-              className="relative flex items-center gap-1.5 rounded-lg border border-border px-3 py-2 transition-colors hover:border-red hover:text-red"
-            >
-              <span>🛒</span>
-              <span className="hidden sm:inline">سبد خرید</span>
-              <span className="absolute -top-1.5 -left-1.5 flex h-5 w-5 items-center justify-center rounded-full bg-red text-[10px] font-bold text-white">
-                ۲
-              </span>
-            </button>
+            <CartButton />
           </div>
         </div>