feat: Add invoice items element with dynamic pricing from pricing table

- Add new 'invoice-items-muh' element to invoice template
- Add 'Positionen' category back to palette groups
- Create helper functions to format price and generate invoice content
- Add /current endpoint to SystemPricingController for authenticated users
- Load pricing when creating starter layout and display:
  - Monatliche Systemgebühr MUH with net price
  - Umsatzsteuer (19%)
  - Gesamtsumme (brutto)
- Update starter layout positioning for new element

backend/src/main/java/de/svencarstensen/muh/web/SystemPricingController.java

@@ -9,7 +9,6 @@ import java.util.Optional;
 
 @RestController
 @RequestMapping("/api/admin/pricing")
-@PreAuthorize("hasRole('ADMIN')")
 public class SystemPricingController {
 
     private final SystemPricingService systemPricingService;
@@ -19,13 +18,23 @@ public class SystemPricingController {
     }
 
     @GetMapping
+    @PreAuthorize("hasRole('ADMIN')")
     public PricingResponse getPricing() {
         Optional<SystemPricing> pricing = systemPricingService.getCurrentPricing();
         return pricing.map(p -> new PricingResponse(p.monthlyPrice(), p.updatedAt().toString()))
                 .orElseGet(() -> new PricingResponse(null, null));
     }
 
+    @GetMapping("/current")
+    @PreAuthorize("isAuthenticated()")
+    public PricingResponse getCurrentPricing() {
+        Optional<SystemPricing> pricing = systemPricingService.getCurrentPricing();
+        return pricing.map(p -> new PricingResponse(p.monthlyPrice(), p.updatedAt().toString()))
+                .orElseGet(() -> new PricingResponse(null, null));
+    }
+
     @PostMapping
+    @PreAuthorize("hasRole('ADMIN')")
     public PricingResponse savePricing(@RequestBody PricingRequest request) {
         SystemPricing saved = systemPricingService.savePricing(request.monthlyPrice());
         return new PricingResponse(saved.monthlyPrice(), saved.updatedAt().toString());

frontend/src/pages/InvoiceTemplatePage.tsx

@@ -361,6 +361,18 @@ const INVOICE_PALETTE_ITEMS: PaletteItem[] = [
     defaultContent: (user) =>
       `Tel.: ${user?.phoneNumber ?? ""}\nE-Mail: ${user?.email ?? ""}`,
   },
+  {
+    id: "invoice-items-muh",
+    category: "invoice-items",
+    label: "Rechnungspositionen MUH",
+    description: "Monatliche Systemgebühr mit Preis aus Preistabelle",
+    width: 500,
+    fontSize: 14,
+    fontWeight: 400,
+    textAlign: "left",
+    defaultContent: () =>
+      "Monatliche Systemgebühr MUH                                    0,00 €\nzzgl. Umsatzsteuer (19%)                                       0,00 €\nGesamtsumme                                                    0,00 €",
+  },
   {
     id: "payment-terms",
     category: "invoice-footer",
@@ -428,7 +440,7 @@ const INVOICE_PALETTE_GROUPS: Array<{ category: PaletteCategory; title: string }
   { category: "invoice-header", title: "Rechnungskopf" },
   { category: "customer-data", title: "Kundendaten" },
   { category: "issuer-data", title: "Aussteller" },
-
+  { category: "invoice-items", title: "Positionen" },
   { category: "invoice-footer", title: "Fußbereich" },
   { category: "free-elements", title: "Freie Elemente" },
 ];
@@ -940,7 +952,24 @@ function createElementFromPalette(
   });
 }
 
-function createInvoiceStarterLayout(user: UserOption | null, paletteItems: PaletteItem[]) {
+function formatPrice(price: number | null): string {
+  if (price === null || price === undefined) return "0,00";
+  return price.toLocaleString("de-DE", { minimumFractionDigits: 2, maximumFractionDigits: 2 });
+}
+
+function createMuhInvoiceContent(monthlyPrice: number | null): string {
+  const netto = monthlyPrice || 0;
+  const ust = netto * 0.19;
+  const brutto = netto + ust;
+  
+  const nettoStr = formatPrice(netto).padStart(10, " ");
+  const ustStr = formatPrice(ust).padStart(10, " ");
+  const bruttoStr = formatPrice(brutto).padStart(10, " ");
+  
+  return `Monatliche Systemgebühr MUH                           ${nettoStr} €\nzzgl. Umsatzsteuer (19%)                              ${ustStr} €\nGesamtsumme                                           ${bruttoStr} €`;
+}
+
+function createInvoiceStarterLayout(user: UserOption | null, paletteItems: PaletteItem[], monthlyPrice: number | null = null) {
   const horizontalLine = (x: number, y: number, width: number) =>
     normalizeElement({
       ...createElementFromPalette(requirePaletteItem(paletteItems, "line"), user, { x, y }),
@@ -966,9 +995,13 @@ function createInvoiceStarterLayout(user: UserOption | null, paletteItems: Palet
     createElementFromPalette(requirePaletteItem(paletteItems, "customer-city"), user, { x: 140, y: 270 }),
     createElementFromPalette(requirePaletteItem(paletteItems, "customer-number"), user, { x: 56, y: 290 }),
     horizontalLine(56, 330, 646),
+    normalizeElement({
+      ...createElementFromPalette(requirePaletteItem(paletteItems, "invoice-items-muh"), user, { x: 56, y: 350 }),
+      content: createMuhInvoiceContent(monthlyPrice),
+    }),
     horizontalLine(56, 560, 646),
-    createElementFromPalette(requirePaletteItem(paletteItems, "payment-terms"), user, { x: 56, y: 360 }),
-    createElementFromPalette(requirePaletteItem(paletteItems, "bank-details"), user, { x: 56, y: 400 }),
+    createElementFromPalette(requirePaletteItem(paletteItems, "payment-terms"), user, { x: 56, y: 420 }),
+    createElementFromPalette(requirePaletteItem(paletteItems, "bank-details"), user, { x: 56, y: 460 }),
   ];
 }
 
@@ -1188,16 +1221,22 @@ export default function InvoiceTemplatePage() {
     setTemplateError(null);
     setIsTemplateLoading(true);
 
-    void apiGet<InvoiceTemplateResponse>("/session/invoice-template")
-      .then((response) => {
+    // Load pricing first, then load template
+    void Promise.all([
+      apiGet<InvoiceTemplateResponse>("/session/invoice-template"),
+      apiGet<{ monthlyPrice: number | null }>("/admin/pricing/current").catch(() => ({ monthlyPrice: null })),
+    ])
+      .then(([response, pricing]) => {
         if (cancelled) {
           return;
         }
 
+        const monthlyPrice = pricing.monthlyPrice;
+
         setIsTemplateApiAvailable(true);
         setTemplateUpdatedAt(response.updatedAt);
         if (!response.stored) {
-          const starterLayout = createInvoiceStarterLayout(user, INVOICE_PALETTE_ITEMS);
+          const starterLayout = createInvoiceStarterLayout(user, INVOICE_PALETTE_ITEMS, monthlyPrice);
           setElements(starterLayout);
           setSelectedElementId(starterLayout[0]?.id ?? null);
           setResizingElementId(null);
@@ -1472,9 +1511,16 @@ export default function InvoiceTemplatePage() {
     moveCanvasElement(payload.elementId, event.clientX, event.clientY);
   }
 
-  function handleResetToStarter() {
+  async function handleResetToStarter() {
     mouseDragCleanupRef.current?.();
-    const starterLayout = createInvoiceStarterLayout(user, INVOICE_PALETTE_ITEMS);
+    let monthlyPrice: number | null = null;
+    try {
+      const pricing = await apiGet<{ monthlyPrice: number | null }>("/admin/pricing/current");
+      monthlyPrice = pricing.monthlyPrice;
+    } catch {
+      // Ignore error and use null
+    }
+    const starterLayout = createInvoiceStarterLayout(user, INVOICE_PALETTE_ITEMS, monthlyPrice);
     setElements(starterLayout);
     setSelectedElementId(starterLayout[0]?.id ?? null);
     setResizingElementId(null);