feat: Split customer address into separate fields in invoice template

Replace combined 'customer-address' with 4 separate elements:
- customer-street (Straße)
- customer-house-number (Hausnummer)
- customer-postal-code (PLZ)
- customer-city (Ort)

Update starter layout to use new separate fields with appropriate positioning.

frontend/src/pages/InvoiceTemplatePage.tsx

@@ -36,7 +36,10 @@ const INVOICE_LOCKED_TEXT_PALETTE_IDS = new Set([
   "invoice-due-date",
   "customer-number",
   "customer-name",
-  "customer-address",
+  "customer-street",
+  "customer-house-number",
+  "customer-postal-code",
+  "customer-city",
   "customer-email",
   "customer-phone",
   "invoice-subtotal",
@@ -225,15 +228,48 @@ const INVOICE_PALETTE_ITEMS: PaletteItem[] = [
     defaultContent: () => "VoS, Dirk Schwissel",
   },
   {
-    id: "customer-address",
+    id: "customer-street",
     category: "customer-data",
-    label: "Kundenadresse",
+    label: "Kunden-Straße",
-    description: "Adresse des Kunden",
+    description: "Straße des Kunden",
-    width: 280,
+    width: 200,
     fontSize: 14,
     fontWeight: 400,
     textAlign: "left",
-    defaultContent: () => "Musterstraße 123\n12345 Musterstadt",
+    defaultContent: () => "Musterstraße",
+  },
+  {
+    id: "customer-house-number",
+    category: "customer-data",
+    label: "Kunden-Hausnummer",
+    description: "Hausnummer des Kunden",
+    width: 80,
+    fontSize: 14,
+    fontWeight: 400,
+    textAlign: "left",
+    defaultContent: () => "123",
+  },
+  {
+    id: "customer-postal-code",
+    category: "customer-data",
+    label: "Kunden-PLZ",
+    description: "Postleitzahl des Kunden",
+    width: 80,
+    fontSize: 14,
+    fontWeight: 400,
+    textAlign: "left",
+    defaultContent: () => "12345",
+  },
+  {
+    id: "customer-city",
+    category: "customer-data",
+    label: "Kunden-Ort",
+    description: "Ort des Kunden",
+    width: 200,
+    fontSize: 14,
+    fontWeight: 400,
+    textAlign: "left",
+    defaultContent: () => "Musterstadt",
   },
   {
     id: "customer-email",
@@ -922,7 +958,10 @@ function createInvoiceStarterLayout(user: UserOption | null, paletteItems: Palet
     createElementFromPalette(requirePaletteItem(paletteItems, "invoice-due-date"), user, { x: 480, y: 148 }),
     horizontalLine(56, 200, 646),
     createElementFromPalette(requirePaletteItem(paletteItems, "customer-name"), user, { x: 56, y: 220 }),
-    createElementFromPalette(requirePaletteItem(paletteItems, "customer-address"), user, { x: 56, y: 246 }),
+    createElementFromPalette(requirePaletteItem(paletteItems, "customer-street"), user, { x: 56, y: 246 }),
+    createElementFromPalette(requirePaletteItem(paletteItems, "customer-house-number"), user, { x: 260, y: 246 }),
+    createElementFromPalette(requirePaletteItem(paletteItems, "customer-postal-code"), user, { x: 56, y: 270 }),
+    createElementFromPalette(requirePaletteItem(paletteItems, "customer-city"), user, { x: 140, y: 270 }),
     createElementFromPalette(requirePaletteItem(paletteItems, "customer-number"), user, { x: 56, y: 290 }),
     horizontalLine(56, 330, 646),
     createElementFromPalette(requirePaletteItem(paletteItems, "invoice-subtotal"), user, { x: 500, y: 460 }),