Add compound tax support (#753)

* test(taxes): cover compound_tax API semantics and validate it as boolean

* feat(taxes): restore the compound tax toggle in tax type settings

* feat(taxes): compute document-level compound tax amounts

Two-pass recalculation: simple taxes on the discounted subtotal, compound
taxes on the subtotal plus all simple taxes (v2 parity; branch order
fixed -> compound -> inclusive back-out -> simple). Amounts now also
recalculate on tax add/remove and on the tax-inclusive toggle, which
previously never triggered recalculation.

* feat(taxes): support compound taxes in per-item mode

Per-item tax rows now carry the compound flag and charge compound taxes
on the item's discounted base plus its simple taxes, through the same
calcTaxAmount branch order as document-level taxes. The item row splits
its tax sums into simple and compound so a compound row can never widen
its own base.

Also fixes two pre-existing bugs: the per-item tax dropdown read
window.__taxTypes, which nothing ever assigned, so it always rendered
empty (tax types are now fetched by the items table and passed down);
and removing a tax row hard-zeroed the item's totals instead of
re-syncing them.

* fix(invoices): skip placeholder tax rows when persisting item taxes

The document form keeps one empty placeholder tax row per item in
per-item tax mode. Its empty name is nullified by the framework's
empty-string middleware, so inserting it violated the NOT NULL
constraint and turned every per-item save into a 500. The equivalent
v2 guard keyed on a null amount, which the v3 stub (amount: 0) evades;
keying on the missing tax_type_id catches it.

resources/scripts/features/shared/document-form/DocumentItemsTable.vue

@@ -92,6 +92,8 @@
             :currency="defaultCurrency"
             :item-validation-scope="itemValidationScope"
             :invoice-items="formData.items"
+            :tax-types="availableTaxTypes"
+            :can-add-tax="canAddTax"
             :store="store"
             :store-prop="storeProp"
           />
@@ -110,11 +112,15 @@
 </template>
 
 <script setup lang="ts">
-import { computed } from 'vue'
+import { computed, onMounted, ref } from 'vue'
 import draggable from 'vuedraggable'
 import DocumentItemRow from './DocumentItemRow.vue'
 import ItemModal from '@/scripts/features/company/items/components/ItemModal.vue'
+import { useUserStore } from '../../../stores/user.store'
+import { taxTypeService } from '../../../api/services/tax-type.service'
+import { ABILITIES } from '../../../config/abilities'
 import type { Currency } from '../../../types/domain/currency'
+import type { TaxType } from '../../../types/domain/tax'
 import type { DocumentFormData } from './use-document-calculations'
 
 interface Props {
@@ -134,6 +140,25 @@ const props = withDefaults(defineProps<Props>(), {
   taxIncludedSetting: 'NO',
 })
 
+const userStore = useUserStore()
+const availableTaxTypes = ref<TaxType[]>([])
+
+const canAddTax = computed<boolean>(() => {
+  return userStore.hasAbilities(ABILITIES.CREATE_TAX_TYPE)
+})
+
+onMounted(async () => {
+  try {
+    const response = await taxTypeService.list({
+      limit: 'all',
+      transaction_type: 'sales',
+    })
+    availableTaxTypes.value = response.data
+  } catch {
+    // Silently fail
+  }
+})
+
 const formData = computed<DocumentFormData>(() => {
   return props.store[props.storeProp] as DocumentFormData
 })