fix: AI visual barcode fallback fires only once per scanner session

If Gemini cannot identify the product visually, mark _aiFallbackExhausted=true
for the current scanner session so the 5s timer never fires again. The scanner
restarts normally (user can keep trying with the barcode reader) and a persistent
status message is shown: 'AI: product not recognized — try scanning the barcode'.
_aiFallbackExhausted resets to false in stopScanner() so the next camera session
starts fresh.

translations/de.json

@@ -223,7 +223,8 @@
     "status_parallel": "Kombinierter Scan aktiv...",
     "ai_fallback_searching": "KI identifiziert Produkt...",
     "ai_fallback_found": "Produkt von KI erkannt",
-    "ai_fallback_not_found": "KI: Produkt nicht erkannt"
+    "ai_fallback_not_found": "KI: Produkt nicht erkannt",
+    "ai_fallback_exhausted": "KI: Produkt nicht erkannt — Barcode erneut scannen"
   },
   "action": {
     "title": "Was möchtest du tun?",

translations/en.json

@@ -223,7 +223,8 @@
     "status_parallel": "Using combined scan methods...",
     "ai_fallback_searching": "AI identifying product...",
     "ai_fallback_found": "Product identified by AI",
-    "ai_fallback_not_found": "AI: product not recognized"
+    "ai_fallback_not_found": "AI: product not recognized",
+    "ai_fallback_exhausted": "AI: product not recognized — try scanning the barcode"
   },
   "action": {
     "title": "What do you want to do?",

translations/es.json

@@ -220,7 +220,8 @@
     "status_parallel": "Escaneo combinado activo...",
     "ai_fallback_searching": "Identificación de IA en curso...",
     "ai_fallback_found": "Producto identificado por IA",
-    "ai_fallback_not_found": "IA: producto no reconocido"
+    "ai_fallback_not_found": "IA: producto no reconocido",
+    "ai_fallback_exhausted": "IA: producto no reconocido — prueba a escanear el código"
   },
   "action": {
     "title": "¿Qué quieres hacer?",

translations/fr.json

@@ -220,7 +220,8 @@
     "status_parallel": "Scan combiné actif...",
     "ai_fallback_searching": "Identification IA en cours...",
     "ai_fallback_found": "Produit identifié par l'IA",
-    "ai_fallback_not_found": "IA : produit non reconnu"
+    "ai_fallback_not_found": "IA : produit non reconnu",
+    "ai_fallback_exhausted": "IA : produit non reconnu — réessayez avec le code-barres"
   },
   "action": {
     "title": "Que voulez-vous faire ?",

translations/it.json

@@ -223,7 +223,8 @@
     "status_parallel": "Doppia scansione attiva...",
     "ai_fallback_searching": "Identificazione AI in corso...",
     "ai_fallback_found": "Prodotto identificato dall'AI",
-    "ai_fallback_not_found": "AI: prodotto non riconosciuto"
+    "ai_fallback_not_found": "AI: prodotto non riconosciuto",
+    "ai_fallback_exhausted": "AI: prodotto non riconosciuto — riprova con il barcode"
   },
   "action": {
     "title": "Cosa vuoi fare?",