fix: disable barcode scanner on web platform

apps/mobile/src/components/ScanFoodModal.tsx

@@ -1,5 +1,5 @@
 import React, { useState, useEffect } from 'react';
-import { View, Text, StyleSheet, Modal, TouchableOpacity, TextInput, Alert } from 'react-native';
+import { View, Text, StyleSheet, Modal, TouchableOpacity, TextInput, Alert, Platform } from 'react-native';
 import { CameraView, useCameraPermissions } from 'expo-camera';
 import { Ionicons } from '@expo/vector-icons';
 import { LinearGradient } from 'expo-linear-gradient';
@@ -111,6 +111,11 @@ export function ScanFoodModal({ visible, onClose, onAddFood }: ScanFoodModalProp
                             <View style={{ width: 28 }} />
                         </View>
 
+                        {Platform.OS === 'web' ? (
+                            <View style={styles.webPlaceholder}>
+                                <Text style={styles.webText}>Barcode scanning is only available on mobile devices</Text>
+                            </View>
+                        ) : (
                             <CameraView
                                 style={styles.camera}
                                 facing="back"
@@ -124,6 +129,7 @@ export function ScanFoodModal({ visible, onClose, onAddFood }: ScanFoodModalProp
                                     <Text style={styles.scanText}>Position barcode within frame</Text>
                                 </View>
                             </CameraView>
+                        )}
                     </>
                 ) : (
                     <View style={styles.resultContainer}>
@@ -230,6 +236,18 @@ const styles = StyleSheet.create({
     camera: {
         flex: 1,
     },
+    webPlaceholder: {
+        flex: 1,
+        justifyContent: 'center',
+        alignItems: 'center',
+        backgroundColor: '#1a1a1a',
+    },
+    webText: {
+        color: '#999',
+        fontSize: 16,
+        textAlign: 'center',
+        paddingHorizontal: 40,
+    },
     scanOverlay: {
         flex: 1,
         justifyContent: 'center',