feat: barcode scan visual feedback + EAN checksum validation

- Add scan-status-bar overlay inside scanner viewport showing:
  - Active scan method (Native API / Quagga / Native + Quagga)
  - Scanning state: ready, scanning, partial read, invalid, confirmed
- Validate EAN-8/EAN-13/UPC checksums in Quagga path before confirming
  (native BarcodeDetector validates internally; Quagga can return false positives)
- Show 'invalid barcode, retrying' message with invalid code highlighted
- Reset invalid barcode confidence counter on invalid read so scanner retries
- Spawn parallel Quagga scan with 'combined scan active' status message
- Add 6 translation keys (scan.status_*) in all 5 language files

assets/css/style.css

@@ -1969,6 +1969,46 @@ body.server-offline .bottom-nav {
     text-overflow: ellipsis;
 }
 
+/* — Scan status bar — */
+.scan-status-bar {
+    position: absolute;
+    bottom: 38px;
+    left: 0;
+    right: 0;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    gap: 2px;
+    pointer-events: none;
+    z-index: 12;
+}
+.scan-status-method {
+    font-size: 0.58rem;
+    color: rgba(255,255,255,0.45);
+    text-transform: uppercase;
+    letter-spacing: 0.07em;
+    font-family: monospace;
+}
+.scan-status-msg {
+    font-size: 0.74rem;
+    color: rgba(255,255,255,0.9);
+    background: rgba(0,0,0,0.55);
+    padding: 3px 10px;
+    border-radius: 12px;
+    text-align: center;
+    max-width: 92%;
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    transition: color 0.2s, background 0.2s;
+    backdrop-filter: blur(3px);
+}
+.scan-status-msg:empty { visibility: hidden; }
+.scan-status-msg.state-partial { color: #fbbf24; }
+.scan-status-msg.state-invalid { color: #f87171; background: rgba(239,68,68,0.28); }
+.scan-status-msg.state-confirmed { color: #4ade80; background: rgba(74,222,128,0.22); }
+.scan-status-msg.state-retry { color: #fb923c; }
+
 /* — Viewport overlay controls (torch / zoom / flip) — */
 .scan-viewport-controls {
     position: absolute;

assets/js/app.js

@@ -6420,6 +6420,9 @@ async function initScanner() {
         // Apply fixed 2x zoom
         await _applyFixedZoom();
 
+        _invalidBarcodeCount = 0;
+        _setScanStatus(t('scan.status_ready'), '', '');
+
         if (_useBarcodeDetector) {
             startNativeScanner(video);
         } else {
@@ -6460,6 +6463,19 @@ function validateEANChecksum(code) {
     return check === last;
 }
 
+// ===== SCAN STATUS BAR =====
+let _invalidBarcodeCount = 0;
+
+function _setScanStatus(msg, state, method) {
+    const msgEl = document.getElementById('scan-status-msg');
+    const methodEl = document.getElementById('scan-status-method');
+    if (msgEl) {
+        msgEl.textContent = msg || '';
+        msgEl.className = 'scan-status-msg' + (state ? ' state-' + state : '');
+    }
+    if (methodEl && method !== undefined) methodEl.textContent = method || '';
+}
+
 // ===== NATIVE BarcodeDetector SCANNER =====
 async function startNativeScanner(videoEl) {
     if (quaggaRunning) return;
@@ -6491,14 +6507,18 @@ async function startNativeScanner(videoEl) {
         if (!scanning || !scannerStream) return;
         frameCount++;
         
-        if (frameCount === 1) updateFeedback('scanning');
+        if (frameCount === 1) {
+            updateFeedback('scanning');
+            _setScanStatus(t('scan.status_scanning'), '', 'Native API');
+        }
 
         // After 2s without detection, also start Quagga in parallel as backup
         if (!quaggaParallelStarted && (Date.now() - startTime) > 2000) {
             quaggaParallelStarted = true;
             scanLog('Native: 2s elapsed, spawning Quagga in parallel');
+            _setScanStatus(t('scan.status_parallel'), 'retry', 'Native + Quagga');
             quaggaRunning = false; // temporarily release so Quagga can start
-            startQuaggaScanner(videoEl);
+            startQuaggaScanner(videoEl, false);
             quaggaRunning = true; // re-take ownership (Quagga will share)
         }
         
@@ -6512,6 +6532,7 @@ async function startNativeScanner(videoEl) {
                 scanLog(`Native detect #${partialCount} [f${frameCount}]: ${code} (${format})`);
                 updateFeedback('detecting');
                 _showScanLiveCode(code);
+                _setScanStatus(t('scan.status_partial').replace('{code}', code), 'partial');
                 
                 if (!detectionHistory[code]) detectionHistory[code] = { count: 0 };
                 detectionHistory[code].count++;
@@ -6531,6 +6552,7 @@ async function startNativeScanner(videoEl) {
                     quaggaRunning = false;
                     updateFeedback(null);
                     scanLog(`CONFIRMED: ${code} after ${frameCount} frames (${format})`);
+                    _setScanStatus(t('scan.status_confirmed'), 'confirmed');
                     onBarcodeDetected(code);
                     return;
                 }
@@ -6553,7 +6575,7 @@ async function startNativeScanner(videoEl) {
 }
 
 // ===== QUAGGA FALLBACK SCANNER =====
-function startQuaggaScanner(videoEl) {
+function startQuaggaScanner(videoEl, isPrimary = true) {
     if (quaggaRunning) return;
     
     const canvas = document.getElementById('scanner-canvas');
@@ -6619,6 +6641,7 @@ function startQuaggaScanner(videoEl) {
         if (frameCount === 1) {
             scanLog(`Frame #1 — video: ${videoEl.videoWidth}x${videoEl.videoHeight}`);
             updateScannerFeedback('scanning');
+            if (isPrimary) _setScanStatus(t('scan.status_scanning'), '', 'Quagga');
         }
         
         let callbackCalled = false;
@@ -6675,15 +6698,26 @@ function startQuaggaScanner(videoEl) {
                     // EAN/UPC: confirm on first hit (checksum validated)
                     const highConf = ['ean_reader','ean_8_reader','upc_reader','upc_e_reader'].includes(format);
                     if (highConf || detectCount >= 2 || dominated.count >= 2) {
+                        // Validate EAN/UPC checksum — Quagga can occasionally return false positives
+                        if (highConf && !validateEANChecksum(code)) {
+                            _invalidBarcodeCount++;
+                            scanLog(`Invalid EAN checksum: ${code} (retry #${_invalidBarcodeCount})`);
+                            _setScanStatus(t('scan.status_invalid').replace('{code}', code), 'invalid', 'Quagga');
+                            lastDetected = ''; detectCount = 0; // reset confidence
+                            if (scanning) setTimeout(scanFrame, 60);
+                            return;
+                        }
                         scanning = false;
                         quaggaRunning = false;
                         updateScannerFeedback(null);
                         scanLog(`CONFIRMED: ${code} [${passName2}] f${frameCount} consec:${detectCount} total:${dominated.count}`);
                         _hideScanLiveCode();
+                        _setScanStatus(t('scan.status_confirmed'), 'confirmed');
                         onBarcodeDetected(code);
                         return;
                     }
                     _showScanLiveCode(code);
+                    _setScanStatus(t('scan.status_partial').replace('{code}', code), 'partial');
                 } else {
                     updateScannerFeedback('scanning');
                 }

index.html

@@ -251,6 +251,11 @@
                 </div>
                 <!-- Live partial code preview -->
                 <div class="scan-live-code" id="scan-live-code" style="display:none"></div>
+                <!-- Scan status bar -->
+                <div class="scan-status-bar" id="scan-status-bar">
+                    <span id="scan-status-method" class="scan-status-method"></span>
+                    <span id="scan-status-msg" class="scan-status-msg" data-i18n="scan.status_ready"></span>
+                </div>
                 <!-- Success flash overlay -->
                 <div class="scan-confirm-overlay" id="scan-confirm-overlay" style="display:none">
                     <div class="scan-confirm-check">✓</div>

translations/de.json

@@ -214,7 +214,13 @@
         "scan_barcode": "🔖 Barcode scannen",
         "create_named": "{name} erstellen",
         "new_without_barcode": "Neues Produkt ohne Barcode",
-        "stock_in_pantry": "Bereits im Vorrat:"
+        "stock_in_pantry": "Bereits im Vorrat:",
+        "status_ready": "Kamera auf Barcode richten",
+        "status_scanning": "Scanne...",
+        "status_partial": "Erkannt: {code} — prüfe...",
+        "status_invalid": "Ungültig: {code} — versuche erneut",
+        "status_confirmed": "Bestätigt!",
+        "status_parallel": "Kombinierter Scan aktiv..."
     },
     "action": {
         "title": "Was möchtest du tun?",

translations/en.json

@@ -214,7 +214,13 @@
         "scan_barcode": "🔖 Scan Barcode",
         "create_named": "Create {name}",
         "new_without_barcode": "New product without barcode",
-        "stock_in_pantry": "Already in pantry:"
+        "stock_in_pantry": "Already in pantry:",
+        "status_ready": "Point camera at barcode",
+        "status_scanning": "Scanning...",
+        "status_partial": "Detected: {code} — verifying...",
+        "status_invalid": "Invalid: {code} — retrying",
+        "status_confirmed": "Confirmed!",
+        "status_parallel": "Using combined scan methods..."
     },
     "action": {
         "title": "What do you want to do?",

translations/es.json

@@ -211,7 +211,13 @@
         "barcode_acquired": "🔖 Código de barras escaneado: {code}",
         "scan_barcode": "🔖 Escanear código de barras",
         "create_named": "Crear {name}",
-        "new_without_barcode": "Nuevo producto sin código de barras"
+        "new_without_barcode": "Nuevo producto sin código de barras",
+        "status_ready": "Apunta la cámara al código de barras",
+        "status_scanning": "Escaneando...",
+        "status_partial": "Detectado: {code} — verificando...",
+        "status_invalid": "Inválido: {code} — reintentando",
+        "status_confirmed": "Confirmado!",
+        "status_parallel": "Escaneo combinado activo..."
     },
     "action": {
         "title": "¿Qué quieres hacer?",

translations/fr.json

@@ -211,7 +211,13 @@
         "barcode_acquired": "🔖 Code-barres scanné : {code}",
         "scan_barcode": "🔖 Scanner le code-barres",
         "create_named": "Créer {name}",
-        "new_without_barcode": "Nouveau produit sans code-barres"
+        "new_without_barcode": "Nouveau produit sans code-barres",
+        "status_ready": "Pointez la caméra sur le code-barres",
+        "status_scanning": "Scan en cours...",
+        "status_partial": "Lu : {code} — vérification...",
+        "status_invalid": "Invalide : {code} — nouvel essai",
+        "status_confirmed": "Confirmé !",
+        "status_parallel": "Scan combiné actif..."
     },
     "action": {
         "title": "Que voulez-vous faire ?",

translations/it.json

@@ -214,7 +214,13 @@
         "scan_barcode": "🔖 Scansiona Barcode",
         "create_named": "Crea {name}",
         "new_without_barcode": "Nuovo prodotto senza barcode",
-        "stock_in_pantry": "Hai gia in dispensa:"
+        "stock_in_pantry": "Hai gia in dispensa:",
+        "status_ready": "Inquadra il codice a barre",
+        "status_scanning": "Scansione in corso...",
+        "status_partial": "Letto: {code} — verifico...",
+        "status_invalid": "Non valido: {code} — riprovo",
+        "status_confirmed": "Confermato!",
+        "status_parallel": "Doppia scansione attiva..."
     },
     "action": {
         "title": "Cosa vuoi fare?",