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/AddItemForm.vue

@@ -0,0 +1,257 @@
+<template>
+  <UCard>
+    <template #header>
+      <div class="flex items-center justify-between">
+        <h3 class="text-lg font-semibold">Add New Item</h3>
+        <UButton 
+          icon="i-heroicons-x-mark" 
+          color="gray" 
+          variant="ghost"
+          @click="$emit('close')"
+        />
+      </div>
+    </template>
+
+    <form @submit.prevent="handleSubmit" class="space-y-4">
+      <!-- Item Name -->
+      <UFormGroup label="Item Name" required>
+        <UInput 
+          v-model="form.name"
+          placeholder="e.g. Whole Milk, Pasta, Tomatoes"
+          size="lg"
+          autofocus
+        />
+      </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"
+            placeholder="1"
+            size="lg"
+          />
+        </UFormGroup>
+
+        <UFormGroup label="Unit" required>
+          <USelect 
+            v-model="form.unit_id"
+            :options="unitOptions"
+            option-attribute="label"
+            value-attribute="value"
+            placeholder="Select unit"
+            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>
+
+      <!-- Tags -->
+      <UFormGroup label="Tags" hint="Optional">
+        <div class="space-y-2">
+          <!-- Selected Tags -->
+          <div v-if="selectedTags.length > 0" class="flex flex-wrap gap-1 mb-2">
+            <UBadge 
+              v-for="tag in selectedTags" 
+              :key="tag.id"
+              :style="{ backgroundColor: tag.color }"
+              class="text-white cursor-pointer"
+              @click="removeTag(tag.id)"
+            >
+              {{ tag.icon }} {{ tag.name }} ✕
+            </UBadge>
+          </div>
+
+          <!-- Tag Selection by Category -->
+          <div v-for="category in tagCategories" :key="category.name" class="space-y-1">
+            <p class="text-xs font-medium text-gray-500 uppercase">{{ category.name }}</p>
+            <div class="flex flex-wrap gap-1">
+              <UButton
+                v-for="tag in category.tags"
+                :key="tag.id"
+                size="xs"
+                :color="isTagSelected(tag.id) ? 'primary' : 'gray'"
+                :variant="isTagSelected(tag.id) ? 'solid' : 'outline'"
+                @click="toggleTag(tag)"
+              >
+                {{ tag.icon }} {{ tag.name }}
+              </UButton>
+            </div>
+          </div>
+        </div>
+      </UFormGroup>
+
+      <!-- Submit -->
+      <div class="flex gap-2 pt-2">
+        <UButton 
+          type="submit"
+          color="primary"
+          size="lg"
+          class="flex-1"
+          :loading="submitting"
+          :disabled="!isValid"
+        >
+          Add Item
+        </UButton>
+        <UButton 
+          color="gray"
+          size="lg"
+          variant="soft"
+          @click="$emit('close')"
+        >
+          Cancel
+        </UButton>
+      </div>
+    </form>
+  </UCard>
+</template>
+
+<script setup lang="ts">
+const { addInventoryItem, addItemTags } = useInventory()
+const { getUnits } = useUnits()
+const { getTags } = useTags()
+
+const emit = defineEmits<{
+  close: []
+  added: [item: any]
+}>()
+
+// Form state
+const form = reactive({
+  name: '',
+  quantity: 1,
+  unit_id: '',
+  expiry_date: '',
+  notes: ''
+})
+
+const submitting = ref(false)
+const selectedTags = ref<any[]>([])
+
+// Load units and tags
+const units = ref<any[]>([])
+const tags = ref<any[]>([])
+
+onMounted(async () => {
+  const [unitsResult, tagsResult] = await Promise.all([
+    getUnits(),
+    getTags()
+  ])
+
+  units.value = unitsResult.data || []
+  tags.value = tagsResult.data || []
+
+  // Set default unit (Piece)
+  const defaultUnit = units.value.find(u => u.abbreviation === 'pc')
+  if (defaultUnit) {
+    form.unit_id = defaultUnit.id
+  }
+})
+
+// Unit options for select
+const unitOptions = computed(() => {
+  const grouped: Record<string, any[]> = {}
+  
+  for (const unit of units.value) {
+    const type = unit.unit_type
+    if (!grouped[type]) grouped[type] = []
+    grouped[type].push({
+      label: `${unit.name} (${unit.abbreviation})`,
+      value: unit.id
+    })
+  }
+
+  return Object.entries(grouped).flatMap(([type, options]) => [
+    { label: `— ${type.charAt(0).toUpperCase() + type.slice(1)} —`, value: '', disabled: true },
+    ...options
+  ])
+})
+
+// Tag categories for display
+const tagCategories = computed(() => {
+  const categories: Record<string, any[]> = {}
+  
+  for (const tag of tags.value) {
+    const cat = tag.category
+    if (!categories[cat]) categories[cat] = []
+    categories[cat].push(tag)
+  }
+
+  return Object.entries(categories).map(([name, tags]) => ({
+    name,
+    tags
+  }))
+})
+
+// Tag selection helpers
+const isTagSelected = (tagId: string) => {
+  return selectedTags.value.some(t => t.id === tagId)
+}
+
+const toggleTag = (tag: any) => {
+  if (isTagSelected(tag.id)) {
+    removeTag(tag.id)
+  } else {
+    selectedTags.value.push(tag)
+  }
+}
+
+const removeTag = (tagId: string) => {
+  selectedTags.value = selectedTags.value.filter(t => t.id !== tagId)
+}
+
+// Validation
+const isValid = computed(() => {
+  return form.name.trim().length > 0 && form.quantity > 0 && form.unit_id
+})
+
+// Submit
+const handleSubmit = async () => {
+  if (!isValid.value) return
+
+  submitting.value = true
+
+  const { data, error } = await addInventoryItem({
+    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 add item: ' + error.message)
+    submitting.value = false
+    return
+  }
+
+  // Add tags if any selected
+  if (data && selectedTags.value.length > 0) {
+    const tagIds = selectedTags.value.map(t => t.id)
+    await addItemTags(data.id, tagIds)
+  }
+
+  emit('added', data)
+  submitting.value = false
+}
+</script>