Add article pack units with Redux-cached company unit list.

Edit amount/unit on the price tile (pc×1 = no pack unit), manage units in a dialog, and keep the default pc unit non-deletable.

src/utils/units.js

@@ -0,0 +1,47 @@
+/** Company default unit created with every article (`ensureDefaultUnit`). */
+export const DEFAULT_UNIT_SI = 'pc';
+
+/**
+ * Common unit presets for the editor UI (not an API).
+ * Selecting a preset upserts via PUT /api/unit when missing.
+ */
+export const COMMON_UNITS = [
+  { si: 'pc', basesi: 'pc', basesifactor: 1, symbol: 'Stk', name: 'Stück' },
+  { si: 'g', basesi: 'g', basesifactor: 1, symbol: 'g', name: 'Gramm' },
+  { si: 'kg', basesi: 'kg', basesifactor: 1, symbol: 'kg', name: 'Kilogramm' },
+  { si: 'ml', basesi: 'l', basesifactor: 0.001, symbol: 'ml', name: 'Milliliter' },
+  { si: 'l', basesi: 'l', basesifactor: 1, symbol: 'L', name: 'Liter' },
+  { si: 'm', basesi: 'm', basesifactor: 1, symbol: 'm', name: 'Meter' },
+  { si: 'cm', basesi: 'm', basesifactor: 0.01, symbol: 'cm', name: 'Zentimeter' },
+];
+
+export function unitLabel(unit) {
+  if (!unit) return '';
+  if (unit.symbol && unit.name) return `${unit.symbol} · ${unit.name}`;
+  return unit.symbol || unit.name || unit.si;
+}
+
+export function findUnitBySi(units, si) {
+  if (!Array.isArray(units) || si == null) return null;
+  return units.find((row) => row.si === si) ?? null;
+}
+
+/** DB default on create: pc × 1 means “no pack unit” in the UI. */
+export function isNoPackUnit(si, amount) {
+  return si === DEFAULT_UNIT_SI && Number(amount) === 1;
+}
+
+export function firstPackUnitSi(units, preferredSi) {
+  const list = Array.isArray(units) ? units : [];
+  if (
+    preferredSi &&
+    preferredSi !== DEFAULT_UNIT_SI &&
+    findUnitBySi(list, preferredSi)
+  ) {
+    return preferredSi;
+  }
+  const nonPc = list.find((row) => row.si !== DEFAULT_UNIT_SI);
+  if (nonPc) return nonPc.si;
+  if (preferredSi && preferredSi !== DEFAULT_UNIT_SI) return preferredSi;
+  return '';
+}