feat: implement scan-to-add flow (#25)

- Create useProductLookup composable
- Integrate real product lookup in scan page
- Add query parameter handling in index.vue
- Pre-fill AddItemForm from scan data
- Parse quantity and unit from product data
- Include barcode and brand in notes

Complete end-to-end scan workflow:
1. Scan barcode
2. Fetch from Open Food Facts
3. Navigate to inventory with data
4. Pre-filled add form
5. One-click add to inventory

Closes #25

app/components/inventory/AddItemForm.vue

@@ -131,6 +131,16 @@ const { addInventoryItem, addItemTags } = useInventory()
 const { getUnits } = useUnits()
 const { getTags } = useTags()
 
+const props = defineProps<{
+  initialData?: {
+    barcode?: string
+    name?: string
+    brand?: string
+    image_url?: string
+    quantity?: string
+  }
+}>()
+
 const emit = defineEmits<{
   close: []
   added: [item: any]
@@ -166,6 +176,40 @@ onMounted(async () => {
   if (defaultUnit) {
     form.unit_id = defaultUnit.id
   }
+
+  // Pre-fill from initial data (scan-to-add flow)
+  if (props.initialData) {
+    if (props.initialData.name) {
+      form.name = props.initialData.name
+    }
+    
+    // Add brand to notes if available
+    if (props.initialData.brand) {
+      form.notes = `Brand: ${props.initialData.brand}`
+      
+      if (props.initialData.barcode) {
+        form.notes += `\nBarcode: ${props.initialData.barcode}`
+      }
+    } else if (props.initialData.barcode) {
+      form.notes = `Barcode: ${props.initialData.barcode}`
+    }
+
+    // Parse quantity if available (e.g., "750g")
+    if (props.initialData.quantity) {
+      const quantityMatch = props.initialData.quantity.match(/^([\d.]+)\s*([a-zA-Z]+)$/)
+      if (quantityMatch) {
+        form.quantity = parseFloat(quantityMatch[1])
+        // Try to match unit
+        const unitAbbr = quantityMatch[2].toLowerCase()
+        const matchedUnit = units.value.find(u => 
+          u.abbreviation.toLowerCase() === unitAbbr
+        )
+        if (matchedUnit) {
+          form.unit_id = matchedUnit.id
+        }
+      }
+    }
+  }
 })
 
 // Unit options for select

app/composables/useProductLookup.ts

@@ -0,0 +1,61 @@
+// Composable for product lookup via Edge Function
+
+export interface ProductData {
+  barcode: string
+  name: string
+  brand?: string
+  quantity?: string
+  image_url?: string
+  category?: string
+  cached?: boolean
+}
+
+export const useProductLookup = () => {
+  const supabase = useSupabaseClient()
+  const isLoading = ref(false)
+  const error = ref<string | null>(null)
+
+  const lookupProduct = async (barcode: string): Promise<ProductData | null> => {
+    isLoading.value = true
+    error.value = null
+
+    try {
+      const { data, error: functionError } = await supabase.functions.invoke('product-lookup', {
+        body: { barcode }
+      })
+
+      if (functionError) {
+        console.error('Product lookup error:', functionError)
+        error.value = functionError.message || 'Failed to lookup product'
+        
+        // Return basic product data even on error
+        return {
+          barcode,
+          name: `Product ${barcode}`,
+          cached: false
+        }
+      }
+
+      return data as ProductData
+
+    } catch (err) {
+      console.error('Unexpected error during product lookup:', err)
+      error.value = err instanceof Error ? err.message : 'Unknown error'
+      
+      // Return basic product data even on error
+      return {
+        barcode,
+        name: `Product ${barcode}`,
+        cached: false
+      }
+    } finally {
+      isLoading.value = false
+    }
+  }
+
+  return {
+    lookupProduct,
+    isLoading: readonly(isLoading),
+    error: readonly(error)
+  }
+}

app/pages/index.vue

@@ -28,7 +28,8 @@
     <div v-if="showAddForm" class="fixed inset-0 z-50 flex items-start justify-center pt-20 px-4 bg-black/50">
       <div class="w-full max-w-lg">
         <AddItemForm 
-          @close="showAddForm = false"
+          :initial-data="prefilledData"
+          @close="handleCloseAddForm"
           @added="handleItemAdded"
         />
       </div>
@@ -56,13 +57,42 @@ definePageMeta({
   layout: 'default'
 })
 
+const route = useRoute()
+const router = useRouter()
+
 const showAddForm = ref(false)
 const editingItem = ref<any>(null)
 const refreshKey = ref(0)
 const inventoryListRef = ref()
+const prefilledData = ref<any>(null)
+
+// Handle scan-to-add flow (Issue #25)
+onMounted(() => {
+  if (route.query.action === 'add') {
+    // Pre-fill data from query params (from scan)
+    prefilledData.value = {
+      barcode: route.query.barcode as string || undefined,
+      name: route.query.name as string || undefined,
+      brand: route.query.brand as string || undefined,
+      image_url: route.query.image_url as string || undefined,
+      quantity: route.query.quantity as string || undefined,
+    }
+    
+    showAddForm.value = true
+    
+    // Clean up URL
+    router.replace({ query: {} })
+  }
+})
+
+const handleCloseAddForm = () => {
+  showAddForm.value = false
+  prefilledData.value = null
+}
 
 const handleItemAdded = (item: any) => {
   showAddForm.value = false
+  prefilledData.value = null
   // Reload the inventory list
   inventoryListRef.value?.reload()
 }

app/pages/scan.vue

@@ -72,49 +72,33 @@ definePageMeta({
 
 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)
 
+// Use product lookup composable
+const { lookupProduct, isLoading: isLookingUp, error: lookupError } = useProductLookup()
+
 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
+  
+  // Fetch product data from Edge Function
+  const data = await lookupProduct(barcode)
+  
+  if (data) {
+    productData.value = data
   }
 }
 
 const addToInventory = () => {
-  // TODO: Implement scan-to-add flow (Issue #25)
-  // Navigate to add form with pre-filled data
+  // Navigate to home page with add form open and pre-filled
   navigateTo({
     path: '/',
     query: {
+      action: 'add',
       barcode: scannedBarcode.value,
-      name: productData.value?.name,
-      brand: productData.value?.brand
+      name: productData.value?.name || undefined,
+      brand: productData.value?.brand || undefined,
+      image_url: productData.value?.image_url || undefined,
+      quantity: productData.value?.quantity || undefined
     }
   })
 }