feat(frontend): add product detail view and navigation

- Create ProductView component with product details display
- Add ProductView.css with responsive styling
- Add product screen to App.jsx screen system
- Pass onNavigateToProduct callback from App to SearchView
- Update ProductResults onSelect to use callback instead of window.location

apps/frontend/src/App.jsx

@@ -2,6 +2,7 @@ import React, { useState, useEffect } from 'react';
 import './App.css';
 import HomeView from './views/HomeView';
 import SearchView from './views/SearchView';
+import ProductView from './views/ProductView';
 import ScannerView from './views/ScannerView';
 import AlertsView from './views/AlertsView';
 import ProfileView from './views/ProfileView';
@@ -19,6 +20,7 @@ function App() {
   const [showSaved, setShowSaved] = useState(false);
   const [badgeCount, setBadgeCount] = useState(0);
   const [prescriptionSearch, setPrescriptionSearch] = useState('');
+  const [productScreen, setProductScreen] = useState(null);
   const [screenSize, setScreenSize] = useState({
     width: window.innerWidth,
     height: window.innerHeight
@@ -180,6 +182,16 @@ function App() {
           currentUser={currentUser}
           onLoginRequest={() => setShowLogin(true)}
           initialQuery={prescriptionSearch}
+          onNavigateToProduct={(source, id) => setProductScreen({ source, id })}
+        />
+      );
+      break;
+    case 'product':
+      activeView = (
+        <ProductView
+          source={productScreen?.source}
+          id={productScreen?.id}
+          onBack={() => { setProductScreen(null); setScreen('search'); }}
         />
       );
       break;

apps/frontend/src/views/ProductView.css

@@ -0,0 +1,102 @@
+.product-view {
+  width: 100%;
+  max-width: 48rem;
+  margin: 0 auto;
+  padding: 1rem var(--margin-main) 2rem;
+  animation: fadeInUp 0.3s ease-out;
+}
+
+.back-btn {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+  padding: 0.5rem 0;
+  margin-bottom: 1rem;
+  background: none;
+  border: none;
+  color: var(--primary, #2563eb);
+  font-size: 0.875rem;
+  font-weight: 500;
+  cursor: pointer;
+}
+
+.back-btn:hover {
+  opacity: 0.8;
+}
+
+.product-loading,
+.product-error {
+  text-align: center;
+  padding: 3rem 1rem;
+  color: var(--on-surface-variant, #6b7280);
+  font-size: 1rem;
+}
+
+.product-header {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  margin-bottom: 1.5rem;
+}
+
+.product-image {
+  width: 120px;
+  height: 120px;
+  object-fit: contain;
+  border-radius: var(--radius-md, 0.75rem);
+  margin-bottom: 1rem;
+}
+
+.source-badge {
+  display: inline-block;
+  padding: 0.25rem 0.75rem;
+  border-radius: 9999px;
+  color: white;
+  font-size: 0.75rem;
+  font-weight: 600;
+}
+
+.product-name {
+  font-size: 1.5rem;
+  font-weight: 700;
+  color: var(--on-surface);
+  text-align: center;
+  margin-bottom: 0.25rem;
+}
+
+.product-brand {
+  font-size: 1rem;
+  color: var(--on-surface-variant, #6b7280);
+  text-align: center;
+  margin-bottom: 1.5rem;
+}
+
+.product-details {
+  background: var(--surface-container-lowest, #f9fafb);
+  border-radius: var(--radius-md, 0.75rem);
+  padding: 1rem;
+}
+
+.detail-row {
+  display: flex;
+  flex-direction: column;
+  gap: 0.25rem;
+  padding: 0.75rem 0;
+  border-bottom: 1px solid var(--outline-variant, #e5e7eb);
+}
+
+.detail-row:last-child {
+  border-bottom: none;
+}
+
+.detail-label {
+  font-size: 0.75rem;
+  font-weight: 600;
+  color: var(--on-surface-variant, #9ca3af);
+  text-transform: uppercase;
+}
+
+.detail-value {
+  font-size: 0.9375rem;
+  color: var(--on-surface);
+}

apps/frontend/src/views/ProductView.jsx

@@ -0,0 +1,126 @@
+import React, { useState, useEffect } from 'react';
+import './ProductView.css';
+
+export default function ProductView({ source, id, onBack }) {
+  const [product, setProduct] = useState(null);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState(null);
+
+  useEffect(() => {
+    loadProduct();
+  }, [source, id]);
+
+  async function loadProduct() {
+    setLoading(true);
+    setError(null);
+    try {
+      const response = await fetch(`/api/products/${source}/${id}`);
+      if (!response.ok) {
+        throw new Error('Producto no encontrado');
+      }
+      const data = await response.json();
+      setProduct(data);
+    } catch (err) {
+      setError(err.message);
+    } finally {
+      setLoading(false);
+    }
+  }
+
+  if (loading) {
+    return (
+      <div className="product-view">
+        <div className="product-loading">Cargando...</div>
+      </div>
+    );
+  }
+
+  if (error) {
+    return (
+      <div className="product-view">
+        <button className="back-btn" onClick={onBack}>
+          <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2">
+            <path d="M19 12H5M12 19l-7-7 7-7" />
+          </svg>
+          Volver
+        </button>
+        <div className="product-error">{error}</div>
+      </div>
+    );
+  }
+
+  if (!product) return null;
+
+  const isCima = product.source === 'cima';
+  const sourceColor = isCima ? '#2563eb' : '#16a34a';
+  const sourceLabel = isCima ? 'CIMA' : 'Open Food Facts';
+
+  return (
+    <div className="product-view">
+      <button className="back-btn" onClick={onBack}>
+        <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2">
+          <path d="M19 12H5M12 19l-7-7 7-7" />
+        </svg>
+        Volver
+      </button>
+
+      <div className="product-header">
+        {product.image_url && (
+          <img src={product.image_url} alt={product.name} className="product-image" />
+        )}
+        <span className="source-badge" style={{ backgroundColor: sourceColor }}>
+          {sourceLabel}
+        </span>
+      </div>
+
+      <h1 className="product-name">{product.name}</h1>
+      <p className="product-brand">{product.brand}</p>
+
+      <div className="product-details">
+        {isCima ? (
+          <>
+            {product.active_ingredient && (
+              <DetailRow label="Principio activo" value={product.active_ingredient} />
+            )}
+            {product.dosage && (
+              <DetailRow label="Dosis" value={product.dosage} />
+            )}
+            {product.form && (
+              <DetailRow label="Forma farmacéutica" value={product.form} />
+            )}
+            {product.prescription && (
+              <DetailRow label="Prescripción" value={product.prescription} />
+            )}
+            {product.commercialized !== undefined && (
+              <DetailRow label="Comercializado" value={product.commercialized ? 'Sí' : 'No'} />
+            )}
+          </>
+        ) : (
+          <>
+            {product.nutriscore && product.nutriscore !== 'not-applicable' && product.nutriscore !== 'unknown' && (
+              <DetailRow label="Nutri-Score" value={product.nutriscore.toUpperCase()} />
+            )}
+            {product.nova_group && (
+              <DetailRow label="NOVA" value={`Grupo ${product.nova_group}`} />
+            )}
+            {product.eco_score && product.eco_score !== 'unknown' && (
+              <DetailRow label="Eco-Score" value={product.eco_score.toUpperCase()} />
+            )}
+            {product.ingredients && (
+              <DetailRow label="Ingredientes" value={product.ingredients} />
+            )}
+          </>
+        )}
+      </div>
+    </div>
+  );
+}
+
+function DetailRow({ label, value }) {
+  return (
+    <div className="detail-row">
+      <span className="detail-label">{label}</span>
+      <span className="detail-value">{value}</span>
+    </div>
+  );
+}

apps/frontend/src/views/SearchView.jsx

@@ -14,7 +14,7 @@ const suggestions = [
   { name: 'Omeprazol', icon: 'emergency_home', color: 'neutral-4' },
 ];
 
-function SearchView({ currentUser, onLoginRequest, initialQuery = '' }) {
+function SearchView({ currentUser, onLoginRequest, initialQuery = '', onNavigateToProduct }) {
   const [searchQuery, setSearchQuery] = useState(initialQuery);
   const [medicines, setMedicines] = useState([]);
   const [products, setProducts] = useState([]);
@@ -331,7 +331,11 @@ function SearchView({ currentUser, onLoginRequest, initialQuery = '' }) {
                 <ProductResults
                   products={products}
                   onSelect={(p) => {
+                    if (onNavigateToProduct) {
+                      onNavigateToProduct(p.source, p.id);
+                    } else {
                       window.location.href = `/product/${p.source}/${p.id}`;
+                    }
                   }}
                 />
               </div>