fix: improve product search robustness

- search-sheets: ne bloque plus sur l'absence d'ID Shopify en col A
- Shopify GraphQL: first:10 + match exact insensible à la casse au lieu de first:1

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

src/app/api/products/search-sheets/route.ts

@@ -50,9 +50,10 @@ export async function GET(req: NextRequest) {
         const refLower = ref.toLowerCase()
         const ugsLower = ugs.toLowerCase()
         const wordBoundary = new RegExp(`(^|[^a-z0-9])${ugsLower.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')}([^a-z0-9]|$)`)
-        const isMatch = ugs && shopifyId && wordBoundary.test(refLower)
+        // Ne requiert pas shopifyId pour le match UGS — ID peut être absent si produit externe
+        const isMatch = ugs && wordBoundary.test(refLower)
 
-        if (isMatch) {
+        if (isMatch && shopifyId) {
           const title = (row[3] ?? '').trim()
           if (!bestMatch || ugs.length > bestMatch.ugsLength) {
             bestMatch = { shopifyId, title, ugsLength: ugs.length }