feat: shopping list pantry hints, barcode multi-API fallback (OPF/beauty/Gemini), README disclaimer

- Shopping list: each item now shows 'Hai già Xg in dispensa' for same-family inventory stock
  - Lazy-loads inventory once per shopping page visit (_getShoppingInventoryCache)
  - Matches by first significant token (same logic as related-stock on action page)
  - Green hint below item badges, dark-mode aware (.shopping-pantry-hint)
- Barcode lookup: added Open Products Facts + Open Beauty Facts as step 3;
  Gemini AI (_barcodeLookupGemini) as final step 4 fallback
- Added stockForName PHP endpoint (stock_for_name action) for future use
- Restored missing function signatures for _offFetchProduct() and saveProduct()
  that were accidentally lost when stockForName was added in a previous session
- Translation: added shopping.pantry_hint in it/en/de

translations/de.json

@@ -213,7 +213,8 @@
     "barcode_acquired": "🔖 Barcode gescannt: {code}",
     "scan_barcode": "🔖 Barcode scannen",
     "create_named": "{name} erstellen",
-    "new_without_barcode": "Neues Produkt ohne Barcode"
+    "new_without_barcode": "Neues Produkt ohne Barcode",
+    "stock_in_pantry": "Bereits im Vorrat:"
   },
   "action": {
     "title": "Was möchtest du tun?",
@@ -474,7 +475,8 @@
     "priority_medium": "Mittel",
     "priority_low": "Niedrig",
     "smart_last_update": "Aktualisiert {time}",
-    "names_already_updated": "Alle Namen sind bereits aktuell"
+    "names_already_updated": "Alle Namen sind bereits aktuell",
+    "pantry_hint": "Bereits zuhause: {qty}"
   },
   "ai": {
     "title": "🤖 KI-Identifikation",