fix: recherche insensible à la casse et aux accents dans tous les filtres

- utils/search.ts : normalize() (NFD + minuscules) + matchesSearch()
- ShoppingPage filteredProducts : matchesSearch sur nom ET marque
- Backend searchProducts : ilike sur nom ET marque (or_)
- Notes FTS : déjà insensible nativement (plainto_tsquery)

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

frontend/src/pages/ShoppingPage.tsx

@@ -1,5 +1,6 @@
 // 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 {
   fetchLists, createList, fetchListDetail, deleteList,
@@ -213,9 +214,10 @@ export default function ShoppingPage() {
   const hasCurrentList = currentList !== null
   const pastLists = allLists.filter(l => l.status === 'done')
 
-  const filteredProducts = products.filter(
-    p => !itemSearch.trim() || p.name.toLowerCase().includes(itemSearch.trim().toLowerCase())
-  )
+  const filteredProducts = products.filter(p => {
+    const term = itemSearch.trim()
+    return !term || matchesSearch(p.name, term) || matchesSearch(p.brand ?? '', term)
+  })
 
   return (
     <div style={{ display: 'flex', flexDirection: 'column', minHeight: '100%' }}>