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.css

@@ -100,3 +100,86 @@
   font-size: 0.9375rem;
   color: var(--on-surface);
 }
+
+.product-pharmacies {
+  margin-top: 2rem;
+}
+
+.pharmacies-loading {
+  text-align: center;
+  padding: 2rem 1rem;
+  color: var(--on-surface-variant, #6b7280);
+  font-size: 0.875rem;
+}
+
+.pharmacies-title {
+  font-size: 1.125rem;
+  font-weight: 600;
+  color: var(--on-surface);
+  margin-bottom: 1rem;
+}
+
+.pharmacies-grid {
+  display: flex;
+  flex-direction: column;
+  gap: 0.75rem;
+}
+
+.product-pharmacy-card {
+  background: var(--surface-container-lowest, #f9fafb);
+  border-radius: var(--radius-md, 0.75rem);
+  padding: 1rem;
+}
+
+.product-pharmacy-name {
+  font-size: 0.9375rem;
+  font-weight: 600;
+  color: var(--on-surface);
+  margin-bottom: 0.25rem;
+}
+
+.product-pharmacy-address {
+  font-size: 0.8125rem;
+  color: var(--on-surface-variant, #6b7280);
+  margin-bottom: 0.25rem;
+}
+
+.product-pharmacy-phone {
+  font-size: 0.8125rem;
+  color: var(--on-surface-variant, #6b7280);
+  margin-bottom: 0.5rem;
+}
+
+.product-pharmacy-status {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+}
+
+.product-pharmacy-price {
+  font-size: 0.9375rem;
+  font-weight: 600;
+  color: var(--primary, #2563eb);
+}
+
+.product-pharmacy-stock {
+  font-size: 0.75rem;
+  font-weight: 600;
+  padding: 0.15rem 0.5rem;
+  border-radius: 9999px;
+}
+
+.product-pharmacy-stock.in-stock {
+  background: #dcfce7;
+  color: #166534;
+}
+
+.product-pharmacy-stock.low-stock {
+  background: #fef9c3;
+  color: #854d0e;
+}
+
+.product-pharmacy-stock.out-of-stock {
+  background: #fee2e2;
+  color: #991b1b;
+}