feat: add pharmacy-product linking system

- Add pharmacy_products table (PostgreSQL + SQLite)
- Add public route GET /api/products/:source/:id/pharmacies
- Add admin CRUD routes for pharmacy-product links
- Add cascade delete when pharmacy is removed
- Update ProductView to show linked pharmacies
- Create PharmacyProductLink admin component
- Add 'Vincular Producto a Farmacia' tab in AdminView

apps/frontend/src/views/ProductView.jsx

@@ -5,6 +5,8 @@ export default function ProductView({ source, id, onBack }) {
   const [product, setProduct] = useState(null);
   const [loading, setLoading] = useState(true);
   const [error, setError] = useState(null);
+  const [pharmacies, setPharmacies] = useState([]);
+  const [loadingPharmacies, setLoadingPharmacies] = useState(false);
 
   useEffect(() => {
     loadProduct();
@@ -13,6 +15,7 @@ export default function ProductView({ source, id, onBack }) {
   async function loadProduct() {
     setLoading(true);
     setError(null);
+    setPharmacies([]);
     try {
       const response = await fetch(`/api/products/${source}/${id}`);
       if (!response.ok) {
@@ -20,6 +23,7 @@ export default function ProductView({ source, id, onBack }) {
       }
       const data = await response.json();
       setProduct(data);
+      loadPharmacies(source, data.id);
     } catch (err) {
       setError(err.message);
     } finally {
@@ -27,6 +31,21 @@ export default function ProductView({ source, id, onBack }) {
     }
   }
 
+  async function loadPharmacies(productSource, productId) {
+    setLoadingPharmacies(true);
+    try {
+      const response = await fetch(`/api/products/${productSource}/${productId}/pharmacies`);
+      if (response.ok) {
+        const data = await response.json();
+        setPharmacies(data);
+      }
+    } catch {
+      // Pharmacies are optional — don't block on failure
+    } finally {
+      setLoadingPharmacies(false);
+    }
+  }
+
   if (loading) {
     return (
       <div className="product-view">
@@ -112,6 +131,41 @@ export default function ProductView({ source, id, onBack }) {
           </>
         )}
       </div>
+
+      <div className="product-pharmacies">
+        {loadingPharmacies ? (
+          <div className="pharmacies-loading">Cargando farmacias...</div>
+        ) : pharmacies.length > 0 ? (
+          <>
+            <h3 className="pharmacies-title">
+              Disponible en {pharmacies.length} {pharmacies.length === 1 ? 'farmacia' : 'farmacias'}
+            </h3>
+            <div className="pharmacies-grid">
+              {pharmacies.map((pharmacy) => (
+                <div key={pharmacy.id} className="product-pharmacy-card">
+                  <h4 className="product-pharmacy-name">{pharmacy.name}</h4>
+                  <p className="product-pharmacy-address">{pharmacy.address}</p>
+                  {pharmacy.phone && (
+                    <p className="product-pharmacy-phone">{pharmacy.phone}</p>
+                  )}
+                  <div className="product-pharmacy-status">
+                    {pharmacy.price && (
+                      <span className="product-pharmacy-price">
+                        {parseFloat(pharmacy.price).toFixed(2)} &euro;
+                      </span>
+                    )}
+                    {pharmacy.stock !== undefined && (
+                      <span className={`product-pharmacy-stock ${pharmacy.stock > 20 ? 'in-stock' : pharmacy.stock > 0 ? 'low-stock' : 'out-of-stock'}`}>
+                        {pharmacy.stock > 20 ? 'En Stock' : pharmacy.stock > 0 ? `Stock Bajo (${pharmacy.stock})` : 'Sin Stock'}
+                      </span>
+                    )}
+                  </div>
+                </div>
+              ))}
+            </div>
+          </>
+        ) : null}
+      </div>
     </div>
   );
 }