feat(mcp): Vorschau von Ausgangsbelegen mit Seitenbildern und Umbruchprüfung

- accounting.outgoing_documents.preview rendert den Beleg wie der Editor und liefert Seiten als PNG-Bilder im MCP-Ergebnis
- Layout je Seite in mm mit Warnungen zu übervollen Seiten, allein stehenden Überschriften, leeren Seiten und vom Überweisungs-QR-Code überdeckten Beträgen samt Vorschlag für den Seitenumbruch
- rows testet geänderte Positionen samt Seitenumbrüchen, ohne zu speichern
- Belegdaten für das PDF als Backend-Port von getDocumentData (Titelsummen, Überträge, Abschläge, Optional-/Alternativpositionen)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/src/utils/pdf.ts

@@ -117,7 +117,17 @@ const getDuration = (time) => {
 }
 
 
-export const createInvoicePDF = async (server:FastifyInstance, returnMode, invoiceData, backgroundPath:string) => {
+/** Positions in mm from the top edge, recorded while rendering for layout checks (e.g. page breaks). */
+export type InvoicePdfLayout = {
+    pageHeightMm: number
+    rows: Array<{ index: number, id?: string, pos?: string, mode: string, text: string, page: number, topMm: number, bottomMm: number }>
+    totals?: { page: number, topMm: number, bottomMm: number }
+    endText?: { page: number, topMm: number, bottomMm: number }
+    paymentQr?: { page: number, topMm: number, leftMm: number }
+    pageCount: number
+}
+
+export const createInvoicePDF = async (server:FastifyInstance, returnMode, invoiceData, backgroundPath:string, layout?: InvoicePdfLayout) => {
     const deliveryNoteLikeDocumentTypes = ["deliveryNotes", "packingSlips"]
     const isPackingSlip = invoiceData?.type === "packingSlips"
 
@@ -496,6 +506,7 @@ export const createInvoicePDF = async (server:FastifyInstance, returnMode, invoi
         }
 
         invoiceData.rows.forEach((row, index) => {
+            const layoutTop = rowHeight
 
             if (!["pagebreak", "title", "text"].includes(row.mode)) {
 
@@ -881,10 +892,16 @@ export const createInvoicePDF = async (server:FastifyInstance, returnMode, invoi
                 }
             }
             console.log(rowHeight)
+            layout?.rows.push({
+                index, id: row.id, pos: row.pos, mode: row.mode, text: String(row.text || "").slice(0, 80),
+                // rowHeight is the baseline of the first text line; shift to the visible cap height.
+                page: pageCounter, topMm: row.mode === "pagebreak" ? 30 : layoutTop - 3, bottomMm: row.mode === "pagebreak" ? 30 : rowHeight - 3,
+            })
         })
 
 
         let endTextDiff = 35
+        const layoutContentEnd = rowHeight
 
         if (!deliveryNoteLikeDocumentTypes.includes(invoiceData.type)) {
             pages[pageCounter - 1].drawLine({
@@ -1001,6 +1018,18 @@ export const createInvoicePDF = async (server:FastifyInstance, returnMode, invoi
 
             const endTextPosition = getCoordinatesForPDFLib(21, rowHeight + endTextDiff + (invoiceData.totalArray.length - 3) * 8, page1)
 
+            if (layout) {
+                const maxWidth = getTextWidthBeforePaymentQr(pages[pageCounter - 1], endTextPosition.x)
+                const lines = String(invoiceData.endText || "").split("\n")
+                    .reduce((sum, line) => sum + Math.max(1, Math.ceil(font.widthOfTextAtSize(line, 10) / maxWidth)), 0)
+                const topMm = rowHeight + endTextDiff + (invoiceData.totalArray.length - 3) * 8
+                // Totals are baselines 8 mm apart; tax notes (13b/19/12.3) add one more line below.
+                const totalLines = invoiceData.totalArray.length + (["13b UStG", "19 UStG", "12.3 UStG"].includes(invoiceData.taxType) ? 1 : 0)
+                layout.totals = { page: pageCounter, topMm: layoutContentEnd, bottomMm: rowHeight + (totalLines - 1) * 8 + 1 }
+                // drawText places the baseline of the first line; 10 pt line height ≈ 3.53 mm.
+                layout.endText = { page: pageCounter, topMm: topMm - 3.53, bottomMm: topMm + (lines - 1) * 3.53 + 1 }
+            }
+
             pages[pageCounter - 1].drawText(invoiceData.endText, {
                 ...endTextPosition,
                 size: 10,
@@ -1030,6 +1059,12 @@ export const createInvoicePDF = async (server:FastifyInstance, returnMode, invoi
                 font: fontBold,
             })
 
+            if (layout) layout.paymentQr = {
+                page: pages.length,
+                topMm: (lastPage.getHeight() - (qrY + qrSize + labelGap + 8)) / mm,
+                leftMm: qrX / mm,
+            }
+
             lastPage.drawImage(paymentQrCode, {
                 x: qrX,
                 y: qrY,
@@ -1038,6 +1073,11 @@ export const createInvoicePDF = async (server:FastifyInstance, returnMode, invoi
             })
         }
 
+        if (layout) {
+            layout.pageCount = pages.length
+            layout.pageHeightMm = page1.getHeight() / mm
+        }
+
         return await pdfDoc.saveAsBase64()
 
     }