feat: enhance forms with decimal formatting and validation

- Updated CustomersPage.vue to use decimalString for standard discount percent.
- Enhanced IncomingInvoicesPage.vue to format item quantities, unit prices, and tax rates using decimalString.
- Improved ItemsPage.vue with new supplier price management and decimal formatting for prices.
- Modified OrganizationSetupPage.vue to use a dropdown for default tax rates and ensure numeric input for payment days.
- Updated OutgoingInvoicesPage.vue to apply decimal formatting for customer discounts and item details.
- Enhanced PriceImportsPage.vue to include additional fields in the import format.
- Improved PriceRulesPage.vue to use decimal input for markup percentages.
- Updated QuotesPage.vue to apply decimal formatting for customer discounts and item details.
- Enhanced SuppliersPage.vue to use decimal input for standard discount percent.
- Added a new SQL migration to set default unit for items to 'Stck'.
- Introduced format.ts for centralized decimal and currency formatting utilities.

web-frontend/src/views/CustomersPage.vue

@@ -3,6 +3,7 @@ import { computed, onMounted, reactive, ref, watch } from "vue";
 import { apiDelete, apiGet, apiPost, apiPut } from "../api";
 import FormStatus from "../components/FormStatus.vue";
 import PageHeader from "../components/PageHeader.vue";
+import { decimalString } from "../format";
 import { matchesObjectSearch, reserveNextNumber } from "../number-ranges";
 import { liveUpdateState } from "../realtime";
 import type { CashDiscountTerm, Customer } from "../types";
@@ -73,9 +74,13 @@ function selectCustomer(customer: Customer) {
 
 async function save() {
   pending.value = true;
+  const payload = {
+    ...form,
+    standard_discount_percent: decimalString(form.standard_discount_percent)
+  };
   const result = selectedId.value
-    ? await apiPut<Customer>(`/api/v1/customers/${encodeURIComponent(selectedId.value)}`, form)
-    : await apiPost<Customer>("/api/v1/customers", form);
+    ? await apiPut<Customer>(`/api/v1/customers/${encodeURIComponent(selectedId.value)}`, payload)
+    : await apiPost<Customer>("/api/v1/customers", payload);
   pending.value = false;
   if (!result.ok) {
     status.value = result.message;
@@ -145,7 +150,7 @@ watch(
               <option value="blocked">Gesperrt</option>
             </select>
           </label>
-          <label class="field"><span>Standardrabatt %</span><input v-model="form.standard_discount_percent" type="number" min="0" max="100" step="0.01" required /></label>
+          <label class="field"><span>Standardrabatt %</span><input v-model="form.standard_discount_percent" inputmode="decimal" required /></label>
           <label class="field">
             <span>Skonto-Regel</span>
             <select v-model="form.cash_discount_term_id">