feat: implement inventory CRUD UI components (#18 #19 #20 #21)

Week 2 core inventory management:

**Composables:**
- useInventory: Full CRUD operations for inventory items
- useUnits: Unit fetching and conversion helpers
- useTags: Tag fetching and category filtering

**Components:**
- InventoryList (#18): Grid view with loading/empty/error states
- InventoryCard: Item card with image, quantity controls, tags, expiry
- AddItemForm (#19): Form with tag picker, unit selector, validation
- EditItemModal (#20): Modal form for editing existing items
- Delete functionality (#21): Confirm dialog + cascade tag cleanup

**Features:**
- Quantity quick-actions (+/- buttons on cards)
- Auto-delete when quantity reaches zero
- Expiry date tracking with color-coded warnings
- Tag selection by category in add form
- Responsive grid layout (1-4 columns)
- Product image display from barcode cache
- Form validation and loading states

Closes #18, #19, #20, #21

app/components/inventory/EditItemModal.vue

@@ -0,0 +1,184 @@
+<template>
+  <UModal v-model="isOpen">
+    <UCard>
+      <template #header>
+        <div class="flex items-center justify-between">
+          <h3 class="text-lg font-semibold">Edit Item</h3>
+          <UButton 
+            icon="i-heroicons-x-mark" 
+            color="gray" 
+            variant="ghost"
+            @click="close"
+          />
+        </div>
+      </template>
+
+      <form @submit.prevent="handleSubmit" class="space-y-4">
+        <!-- Item Name -->
+        <UFormGroup label="Item Name" required>
+          <UInput 
+            v-model="form.name"
+            placeholder="Item name"
+            size="lg"
+          />
+        </UFormGroup>
+
+        <!-- Quantity & Unit -->
+        <div class="grid grid-cols-2 gap-3">
+          <UFormGroup label="Quantity" required>
+            <UInput 
+              v-model.number="form.quantity"
+              type="number"
+              min="0.01"
+              step="0.01"
+              size="lg"
+            />
+          </UFormGroup>
+
+          <UFormGroup label="Unit" required>
+            <USelect 
+              v-model="form.unit_id"
+              :options="unitOptions"
+              option-attribute="label"
+              value-attribute="value"
+              size="lg"
+            />
+          </UFormGroup>
+        </div>
+
+        <!-- Expiry Date -->
+        <UFormGroup label="Expiry Date" hint="Optional">
+          <UInput 
+            v-model="form.expiry_date"
+            type="date"
+            size="lg"
+          />
+        </UFormGroup>
+
+        <!-- Notes -->
+        <UFormGroup label="Notes" hint="Optional">
+          <UTextarea
+            v-model="form.notes"
+            placeholder="Any additional notes..."
+            :rows="2"
+          />
+        </UFormGroup>
+
+        <!-- Submit -->
+        <div class="flex gap-2 pt-2">
+          <UButton 
+            type="submit"
+            color="primary"
+            size="lg"
+            class="flex-1"
+            :loading="submitting"
+            :disabled="!isValid"
+          >
+            Save Changes
+          </UButton>
+          <UButton 
+            color="gray"
+            size="lg"
+            variant="soft"
+            @click="close"
+          >
+            Cancel
+          </UButton>
+        </div>
+      </form>
+    </UCard>
+  </UModal>
+</template>
+
+<script setup lang="ts">
+const { updateInventoryItem } = useInventory()
+const { getUnits } = useUnits()
+
+const props = defineProps<{
+  item: any | null
+}>()
+
+const emit = defineEmits<{
+  close: []
+  updated: [item: any]
+}>()
+
+const isOpen = ref(false)
+const submitting = ref(false)
+const units = ref<any[]>([])
+
+const form = reactive({
+  name: '',
+  quantity: 1,
+  unit_id: '',
+  expiry_date: '',
+  notes: ''
+})
+
+// Load units
+onMounted(async () => {
+  const { data } = await getUnits()
+  units.value = data || []
+})
+
+// Unit options for select
+const unitOptions = computed(() => {
+  return units.value.map(unit => ({
+    label: `${unit.name} (${unit.abbreviation})`,
+    value: unit.id
+  }))
+})
+
+// Watch for item changes (open modal)
+watch(() => props.item, (newItem) => {
+  if (newItem) {
+    form.name = newItem.name
+    form.quantity = Number(newItem.quantity)
+    form.unit_id = newItem.unit_id
+    form.expiry_date = newItem.expiry_date || ''
+    form.notes = newItem.notes || ''
+    isOpen.value = true
+  }
+}, { immediate: true })
+
+// Watch modal close
+watch(isOpen, (val) => {
+  if (!val) {
+    emit('close')
+  }
+})
+
+// Validation
+const isValid = computed(() => {
+  return form.name.trim().length > 0 && form.quantity > 0 && form.unit_id
+})
+
+const close = () => {
+  isOpen.value = false
+}
+
+// Submit
+const handleSubmit = async () => {
+  if (!isValid.value || !props.item) return
+
+  submitting.value = true
+
+  const { data, error } = await updateInventoryItem(props.item.id, {
+    name: form.name.trim(),
+    quantity: form.quantity,
+    unit_id: form.unit_id,
+    expiry_date: form.expiry_date || null,
+    notes: form.notes.trim() || null
+  })
+
+  if (error) {
+    alert('Failed to update item: ' + error.message)
+    submitting.value = false
+    return
+  }
+
+  emit('updated', data)
+  submitting.value = false
+  close()
+}
+</script>