Add editable article prices with gross input and staffel tiers.

Wire PUT /prices, de-DE formatting, tax/staffel pills, and keep the category list cache in sync after photo/price updates.

src/utils/price.js

@@ -1,11 +1,54 @@
+const PRICE_LOCALE = 'de-DE';
+
 export function getBrutto(netto, kSteuerklasse) {
   const rate = { 1: 19, 2: 7, 3: 0 }[kSteuerklasse] ?? 19;
   return netto * (1 + rate / 100);
 }
 
+/** Currency display, e.g. `6,60 €`. */
 export function formatPrice(amount) {
-  return new Intl.NumberFormat('de-DE', {
+  if (amount == null || !Number.isFinite(Number(amount))) return '';
+  return new Intl.NumberFormat(PRICE_LOCALE, {
     style: 'currency',
     currency: 'EUR',
   }).format(amount);
 }
+
+/**
+ * Amount without currency symbol (for fields with a separate € adornment).
+ * e.g. `6,60` / `1.234,56`
+ */
+export function formatPriceAmount(amount, { minFractionDigits = 2, maxFractionDigits = 2 } = {}) {
+  if (amount == null || !Number.isFinite(Number(amount))) return '';
+  return new Intl.NumberFormat(PRICE_LOCALE, {
+    minimumFractionDigits: minFractionDigits,
+    maximumFractionDigits: maxFractionDigits,
+  }).format(amount);
+}
+
+/**
+ * Parse de-DE (or plain) price input → number.
+ * Accepts `6,60`, `1.234,56`, and plain `6.60`.
+ */
+export function parsePriceInput(value) {
+  if (value === '' || value == null) return null;
+  let normalized = String(value).trim().replace(/\s/g, '');
+  if (normalized === '') return null;
+
+  if (normalized.includes(',')) {
+    // de-DE: thousand `.`, decimal `,`
+    normalized = normalized.replace(/\./g, '').replace(',', '.');
+  }
+
+  const parsed = Number(normalized);
+  return Number.isFinite(parsed) && parsed >= 0 ? parsed : null;
+}
+
+/** Convert gross (brutto) → net for PUT /prices. Rounded to 4 decimal places. */
+export function netFromGross(gross, taxRate) {
+  if (gross == null || taxRate == null) return null;
+  if (!Number.isFinite(gross) || !Number.isFinite(taxRate) || taxRate < 0) return null;
+  const factor = 1 + taxRate / 100;
+  if (factor <= 0) return null;
+  return Math.round((gross / factor) * 10000) / 10000;
+}