feat(inventory): add spare parts management

frontend/athena/components/inventory/inventory-utils.ts

@@ -0,0 +1,62 @@
+import type { InventoryItemPayload } from "@/types/inventory";
+
+export function getErrorMessage(error: unknown) {
+  if (typeof error === "object" && error !== null && "response" in error) {
+    const response = (error as { response?: { data?: { detail?: string; message?: string } } }).response;
+    return response?.data?.detail ?? response?.data?.message ?? "Aktion konnte nicht abgeschlossen werden";
+  }
+  return "Aktion konnte nicht abgeschlossen werden";
+}
+
+export function formatDate(value: string) {
+  return new Intl.DateTimeFormat("de-DE", { dateStyle: "short", timeStyle: "short" }).format(new Date(value));
+}
+
+export function formatMoney(cents: number | null, currency = "EUR") {
+  if (cents === null) {
+    return "Keine Angabe";
+  }
+  return new Intl.NumberFormat("de-DE", { style: "currency", currency }).format(cents / 100);
+}
+
+export function euroToCents(value: string) {
+  const normalized = value.trim().replace(",", ".");
+  if (!normalized) {
+    return null;
+  }
+  const amount = Number(normalized);
+  if (!Number.isFinite(amount) || amount < 0) {
+    return null;
+  }
+  return Math.round(amount * 100);
+}
+
+export function centsToEuroInput(cents: number | null) {
+  if (cents === null) {
+    return "";
+  }
+  return (cents / 100).toFixed(2).replace(".", ",");
+}
+
+export const emptyItemPayload: InventoryItemPayload = {
+  sku: null,
+  name: "",
+  description: null,
+  category_id: null,
+  manufacturer: null,
+  manufacturer_part_number: null,
+  supplier_id: null,
+  supplier_part_number: null,
+  compatible_devices: null,
+  location_id: null,
+  quantity_on_hand: 0,
+  quantity_reserved: 0,
+  reorder_level: 0,
+  unit: "Stk.",
+  purchase_price_cents: null,
+  selling_price_cents: null,
+  currency: "EUR",
+  tax_rate_percent: "19.00",
+  notes: null,
+  is_active: true,
+};