feat: add low-stock threshold field to AddItemForm (#67)

app/components/inventory/AddItemForm.vue

@@ -57,6 +57,21 @@
         />
       </UFormGroup>
 
+      <!-- Low Stock Threshold -->
+      <UFormGroup 
+        label="Low Stock Alert" 
+        hint="Optional - Alert when quantity falls below this"
+      >
+        <UInput 
+          v-model.number="form.low_stock_threshold"
+          type="number"
+          min="0"
+          step="0.1"
+          placeholder="e.g. 2"
+          size="lg"
+        />
+      </UFormGroup>
+
       <!-- Notes -->
       <UFormGroup label="Notes" hint="Optional">
         <UTextarea
@@ -121,6 +136,7 @@ const form = reactive({
   quantity: 1,
   unit_id: '',
   expiry_date: '',
+  low_stock_threshold: null as number | null,
   notes: ''
 })
 
@@ -210,6 +226,7 @@ const handleSubmit = async () => {
     quantity: form.quantity,
     unit_id: form.unit_id,
     expiry_date: form.expiry_date || null,
+    low_stock_threshold: form.low_stock_threshold,
     notes: form.notes.trim() || null
   })