feat: integrate BarcodeScanner into scan page (#22 #23)

- Use ScanBarcodeScanner component in scan.vue
- Add product lookup placeholder (Issue #24)
- Add scan-to-add flow placeholder (Issue #25)
- Handle barcode detection events
- Show loading and error states
- Allow rescan and manual entry

Closes #22, #23

app/pages/scan.vue

@@ -2,25 +2,64 @@
   <div>
     <h1 class="text-3xl font-bold text-gray-900 mb-6">Scan Item</h1>
     
-    <UCard>
-      <div class="text-center py-12">
-        <UIcon 
-          name="i-heroicons-qr-code" 
-          class="w-16 h-16 text-gray-400 mx-auto mb-4"
+    <UCard v-if="!scannedBarcode" class="mb-6">
+      <ScanBarcodeScanner 
+        @barcode-detected="handleBarcodeDetected"
+        @manual-entry="showManualEntry = true"
+      />
+    </UCard>
+
+    <!-- Product Lookup Result -->
+    <UCard v-if="productData" class="mb-6">
+      <div class="space-y-4">
+        <div class="flex items-start gap-4">
+          <img 
+            v-if="productData.image_url" 
+            :src="productData.image_url" 
+            :alt="productData.name"
+            class="w-24 h-24 object-cover rounded"
+          />
+          <div class="flex-1">
+            <h3 class="text-xl font-bold mb-1">{{ productData.name }}</h3>
+            <p v-if="productData.brand" class="text-gray-600">{{ productData.brand }}</p>
+            <p class="text-sm text-gray-500 mt-2">Barcode: {{ scannedBarcode }}</p>
+          </div>
+        </div>
+
+        <UAlert 
+          v-if="lookupError"
+          color="yellow" 
+          icon="i-heroicons-exclamation-triangle"
+          title="Product not found"
+          :description="lookupError"
         />
-        <h3 class="text-lg font-semibold text-gray-900 mb-2">
-          Barcode Scanner
-        </h3>
-        <p class="text-gray-600 mb-6">
-          This feature will be implemented in Week 3.
-        </p>
-        <UButton 
-          to="/" 
-          color="gray"
-          variant="soft"
-        >
-          Back to Inventory
-        </UButton>
+
+        <div class="flex gap-2">
+          <UButton 
+            color="primary" 
+            size="lg"
+            icon="i-heroicons-plus"
+            class="flex-1"
+            @click="addToInventory"
+          >
+            Add to Inventory
+          </UButton>
+          <UButton 
+            color="gray" 
+            size="lg"
+            @click="resetScanner"
+          >
+            Scan Again
+          </UButton>
+        </div>
+      </div>
+    </UCard>
+
+    <!-- Loading State -->
+    <UCard v-if="isLookingUp">
+      <div class="text-center py-8">
+        <div class="inline-block animate-spin rounded-full h-12 w-12 border-b-2 border-primary-500 mb-4"></div>
+        <p class="text-gray-600">Looking up product...</p>
       </div>
     </UCard>
   </div>
@@ -30,4 +69,60 @@
 definePageMeta({
   layout: 'default'
 })
+
+const scannedBarcode = ref<string | null>(null)
+const productData = ref<any>(null)
+const isLookingUp = ref(false)
+const lookupError = ref<string | null>(null)
+const showManualEntry = ref(false)
+
+const handleBarcodeDetected = async (barcode: string) => {
+  scannedBarcode.value = barcode
+  lookupError.value = null
+  isLookingUp.value = true
+
+  try {
+    // TODO: Implement product lookup via Edge Function (Issue #24)
+    // For now, create a basic product object
+    await new Promise(resolve => setTimeout(resolve, 1000)) // Simulate API call
+    
+    productData.value = {
+      name: `Product ${barcode}`,
+      brand: 'Unknown Brand',
+      barcode: barcode,
+      image_url: null
+    }
+    
+    lookupError.value = 'Product lookup not yet implemented. Using default data.'
+  } catch (error) {
+    console.error('Product lookup error:', error)
+    lookupError.value = 'Failed to look up product. You can still add it manually.'
+    productData.value = {
+      name: `Product ${barcode}`,
+      barcode: barcode
+    }
+  } finally {
+    isLookingUp.value = false
+  }
+}
+
+const addToInventory = () => {
+  // TODO: Implement scan-to-add flow (Issue #25)
+  // Navigate to add form with pre-filled data
+  navigateTo({
+    path: '/',
+    query: {
+      barcode: scannedBarcode.value,
+      name: productData.value?.name,
+      brand: productData.value?.brand
+    }
+  })
+}
+
+const resetScanner = () => {
+  scannedBarcode.value = null
+  productData.value = null
+  lookupError.value = null
+  isLookingUp.value = false
+}
 </script>