feat(shopping): stats achat produit + édition quantité article

Backend :
- Migration 004 : last_purchased_at (DATE) + avg_interval_days (NUMERIC)
  sur shopping.products
- update_item : met à jour les stats au premier cochage d'un article
  lié à un produit (moyenne mobile exp. 70/30)
- ProductResponse expose les deux nouveaux champs

Frontend :
- ItemRow : long press 500ms → onEdit() (mobile) ; crayon + croix (laptop)
- ShoppingPage : modal édition quantité/unité, état editingItem
- api/shopping.ts : Product inclut last_purchased_at + avg_interval_days

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/ShoppingPage.tsx

@@ -1,7 +1,7 @@
 // frontend/src/pages/ShoppingPage.tsx
 import { useState, useEffect, useCallback } from 'react'
 import { matchesSearch } from '../utils/search'
-import type { ShoppingListDetail, ShoppingList, Store, Product } from '../api/shopping'
+import type { ShoppingListDetail, ShoppingList, Store, Product, ShoppingItem } from '../api/shopping'
 import {
   fetchLists, createList, fetchListDetail, deleteList,
   addItem, updateItem, deleteItem, finishShopping, fetchStores, generateMagicList,
@@ -40,6 +40,9 @@ export default function ShoppingPage() {
   const [showHistoryModal, setShowHistoryModal] = useState(false)
   const [showCatalogueModal, setShowCatalogueModal] = useState(false)
   const [showBoutiquesModal, setShowBoutiquesModal] = useState(false)
+  const [editingItem, setEditingItem] = useState<ShoppingItem | null>(null)
+  const [editQty, setEditQty] = useState('')
+  const [editUnit, setEditUnit] = useState('')
 
   const [itemSearch, setItemSearch] = useState('')
   const [selectedProduct, setSelectedProduct] = useState<Product | null>(null)
@@ -172,6 +175,26 @@ export default function ShoppingPage() {
     }
   }
 
+  function openEditItem(item: ShoppingItem) {
+    setEditingItem(item)
+    setEditQty(item.quantity ?? '')
+    setEditUnit(item.unit ?? '')
+  }
+
+  async function handleEditItem() {
+    if (!currentList || !editingItem) return
+    try {
+      await updateItem(currentList.id, editingItem.id, {
+        quantity: editQty || undefined,
+        unit: editUnit || undefined,
+      })
+      setEditingItem(null)
+      void refreshCurrentList()
+    } catch {
+      setError('Erreur lors de la modification')
+    }
+  }
+
   async function handleFinish() {
     if (!currentList) return
     try {
@@ -367,6 +390,7 @@ export default function ShoppingPage() {
                 item={item}
                 onCheck={() => void handleCheckItem(item.id, true)}
                 onDelete={() => void handleDeleteItem(item.id)}
+                onEdit={() => openEditItem(item)}
                 storeMode
               />
             ))}
@@ -390,6 +414,7 @@ export default function ShoppingPage() {
                     item={item}
                     onCheck={() => void handleCheckItem(item.id, false)}
                     onDelete={() => void handleDeleteItem(item.id)}
+                    onEdit={() => openEditItem(item)}
                     storeMode
                   />
                 ))}
@@ -414,6 +439,41 @@ export default function ShoppingPage() {
 
       {/* ── Modals ── */}
 
+      {/* Modal édition quantité/unité */}
+      {editingItem && (
+        <Modal title={`Modifier — ${editingItem.display_name}`} onClose={() => setEditingItem(null)} width={320}>
+          <div style={{ display: 'flex', flexDirection: 'column', gap: 10 }}>
+            <div style={{ display: 'grid', gridTemplateColumns: '1fr 1fr', gap: 8 }}>
+              <input
+                style={inputStyle}
+                placeholder="Quantité"
+                value={editQty}
+                onChange={e => setEditQty(e.target.value)}
+                autoFocus
+                onKeyDown={e => e.key === 'Enter' && void handleEditItem()}
+              />
+              <input
+                style={inputStyle}
+                placeholder="Unité (kg, L…)"
+                value={editUnit}
+                onChange={e => setEditUnit(e.target.value)}
+                onKeyDown={e => e.key === 'Enter' && void handleEditItem()}
+              />
+            </div>
+            <div style={{ display: 'flex', gap: 8, justifyContent: 'flex-end' }}>
+              <button
+                onClick={() => setEditingItem(null)}
+                style={{ padding: '10px 16px', borderRadius: 8, border: '1px solid var(--bg-5)', background: 'transparent', color: 'var(--ink-2)', cursor: 'pointer', fontFamily: 'var(--font-ui)', minHeight: 48 }}
+              >Annuler</button>
+              <button
+                onClick={() => void handleEditItem()}
+                style={{ padding: '10px 20px', borderRadius: 8, border: 'none', background: 'var(--accent)', color: '#1d2021', cursor: 'pointer', fontFamily: 'var(--font-ui)', fontWeight: 600, minHeight: 48 }}
+              >Enregistrer</button>
+            </div>
+          </div>
+        </Modal>
+      )}
+
       {showAddItemModal && (
         <Modal title="Ajouter un article" onClose={closeAddItemModal} width={420}>
           {/* Barre de recherche / nom personnalisé */}