Task #19: Donation cart (سلة تبرعاتك) for EHSAN POC

Built a real donation cart matching ehsan.sa:
- CartContext provider (localStorage-persisted, defensive parsing) wired into App.tsx
- OpportunityCard: cart icon now adds the case with its typed amount and swaps the
  action row to an added state («مضاف لسلة تبرعاتك» + «إزالة»)
- Header cart button: live count badge + navigates to /cart
- New /cart page + route: breadcrumb, item list (delete icon, category, name,
  editable «قيمة المبلغ» amount, image+progress%), summary panel «الإجمالي» +
  green «للمتابعة للدفع», decorative leaf SVG background, empty state
- translations.ts: parallel AR+EN `cart` section
- donate.tsx: removes the donated case from the cart on successful donation
  (cart reconciliation), preventing stale added-state/badge

Notes/deviations:
- Checkout handoff routes the first cart item into the existing single-case donate
  flow (the POC backend has no multi-item payment). Reconciliation keeps remaining
  items coherent. A true multi-item checkout backend was out of scope.
- Verified with passing e2e test (add → badge → cart page → remove → empty) and
  clean tsc; architect review addressed (reconciliation + defensive parsing).

artifacts/ehsan-poc/src/components/layout/Header.tsx

@@ -2,6 +2,7 @@ import { useEffect, useRef, useState } from "react";
 import { Link, useLocation } from "wouter";
 import { useLanguage } from "../../contexts/LanguageContext";
 import { useAuth } from "../../contexts/AuthContext";
+import { useCart } from "../../contexts/CartContext";
 import { Button } from "../ui/button";
 import {
   Search,
@@ -29,6 +30,7 @@ import ehsanLogo from "../../assets/ehsan-logo.png";
 export function Header() {
   const { language, setLanguage, t } = useLanguage();
   const { isAuthenticated, logout } = useAuth();
+  const { count: cartCount } = useCart();
   const [location, setLocation] = useLocation();
   const [mobileOpen, setMobileOpen] = useState(false);
   const [servicesOpen, setServicesOpen] = useState(false);
@@ -218,11 +220,20 @@ export function Header() {
           <Button
             variant="ghost"
             size="icon"
-            className="text-foreground"
+            className="text-foreground relative"
             aria-label={t.common.cart}
+            onClick={() => setLocation("/cart")}
             data-testid="button-cart"
           >
             <ShoppingCart className="w-4 h-4" />
+            {cartCount > 0 && (
+              <span
+                className="absolute -top-1 -end-1 min-w-[1.1rem] h-[1.1rem] px-1 rounded-full bg-primary text-primary-foreground text-[0.65rem] font-bold flex items-center justify-center leading-none"
+                data-testid="badge-cart-count"
+              >
+                {cartCount}
+              </span>
+            )}
           </Button>
           <Button
             variant="ghost"