feat: allow manual input tax adjustments

frontend/pages/incomingInvoices/[mode]/[id].vue

@@ -194,6 +194,16 @@ const totalCalculated = computed(() => {
 const hasAmount = (value) => value !== null && value !== undefined && value !== ""
 const hasValidNumber = (value) => hasAmount(value) && Number.isFinite(Number(value))
 const isDepreciationItem = (item) => isDepreciationBookingMode(item?.bookingMode)
+const getCalculatedTax = (item) => {
+  const taxRate = Number(taxOptions.value.find((tax) => tax.key === item.taxType)?.percentage || 0)
+
+  return Number((Number(item.amountNet || 0) * (taxRate / 100)).toFixed(2))
+}
+const hasManualTaxDifference = (item) => {
+  if (!hasValidNumber(item.amountTax) || !hasValidNumber(item.amountNet)) return false
+
+  return Math.abs(Number(item.amountTax) - getCalculatedTax(item)) >= 0.005
+}
 
 const updateBookingMode = (item) => {
   ensureDepreciationDefaults(item, itemInfo.value.date)
@@ -216,6 +226,14 @@ const recalculateItem = (item, source) => {
     calculateFromNet()
   } else if (source === 'gross') {
     calculateFromGross()
+  } else if (source === 'tax') {
+    if(!hasValidNumber(item.amountTax)) return
+
+    if((useNetMode.value || !hasAmount(item.amountGross)) && hasAmount(item.amountNet)) {
+      item.amountGross = Number((Number(item.amountNet) + Number(item.amountTax)).toFixed(2))
+    } else if(hasAmount(item.amountGross)) {
+      item.amountNet = Number((Number(item.amountGross) - Number(item.amountTax)).toFixed(2))
+    }
   } else if (source === 'taxType' || source === 'manual') {
     if(hasAmount(item.amountNet)) calculateFromNet()
     else if(hasAmount(item.amountGross)) calculateFromGross()
@@ -871,13 +889,30 @@ const hasBlockingIncomingInvoiceErrors = computed(() => blockingIncomingInvoiceE
                 </div>
 
                 <div class="col-span-6 md:col-span-3">
-                  <UFormField label="Steuerbetrag" help="Automatisch berechnet">
+                  <UFormField label="Steuerbetrag" help="Kann bei Rundungsabweichungen angepasst werden">
-                    <UInput class="w-full" :model-value="item.amountTax" disabled color="gray" >
+                    <UInput
+                        class="w-full"
+                        type="number"
+                        step="0.01"
+                        :model-value="item.amountTax"
+                        :disabled="mode === 'show'"
+                        @update:model-value="(val) => { item.amountTax = Number(val); recalculateItem(item, 'tax') }"
+                    >
                       <template #trailing>€</template>
                     </UInput>
                   </UFormField>
                 </div>
 
+                <div v-if="hasManualTaxDifference(item)" class="col-span-12">
+                  <UAlert
+                      color="warning"
+                      variant="soft"
+                      icon="i-heroicons-exclamation-triangle"
+                      title="Steuerbetrag manuell angepasst"
+                      description="FEDEO verwendet diesen Betrag für Auswertungen und Summen. Im DATEV-Export wird bei der Automatikbuchung nur der Bruttobetrag mit Steuerschlüssel übertragen; DATEV berechnet die Steuer dort erneut."
+                  />
+                </div>
+
                 <div class="col-span-12 flex justify-end gap-2">
                   <UButton
                       size="xs"