fix: negate expense amounts and stop blank trailing pages in cashbox PDF export

Expenses were stored as positive amounts (DB convention) and buildRows()
never negated them, so they were added to the running budget total
instead of subtracted. Negate expense amounts for team-wallet
transactions, mirroring the existing signedFlowAmount() convention in
teams.service.ts.

Separately, addFooters() placed footer text inside the reserved bottom
margin without an explicit height option, which made pdfkit's
LineWrapper treat every footer draw as overflowing the page and call
continueOnNewPage() twice per page - inflating page counts 3x with
blank trailing pages. Bounding the footer text to its own small height
box prevents pdfkit's automatic pagination from firing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

myteamwallet_backend/src/cashbox-export/cashbox-export.utils.spec.ts

@@ -1,5 +1,11 @@
 import { buildCsv, buildPdf, buildReceivableRows, buildRows } from './cashbox-export.utils';
 
+function pdfPageCount(buffer: Buffer): number {
+  const match = buffer.toString('latin1').match(/\/Type\s*\/Pages[\s\S]{0,80}?\/Count\s+(\d+)/);
+  if (!match) throw new Error('Could not find page count in PDF buffer');
+  return Number(match[1]);
+}
+
 describe('buildRows', () => {
   const team = (overrides: Partial<{ transactions: any[]; players: any[] }> = {}) => ({
     id: 5,
@@ -10,12 +16,15 @@ describe('buildRows', () => {
     ...overrides,
   });
 
-  it('includes team-wallet credit and expense rows as "Teamkasse"', () => {
+  it('includes team-wallet credit rows as-is and negates expense rows so they reduce the budget', () => {
+    // DB stores TeamWalletTransaction.amount as a positive number even for
+    // expenses (see team-wallet-transaction.entity.ts setBalance()); buildRows
+    // must negate expenses itself so they subtract from the running total.
     const rows = buildRows(
       team({
         transactions: [
           { date: '2026-08-05T00:00:00.000Z', amount: 100, note: 'Sponsoring', type: { name: 'credit' } },
-          { date: '2026-08-10T00:00:00.000Z', amount: -20, note: 'Bälle', type: { name: 'expense' } },
+          { date: '2026-08-10T00:00:00.000Z', amount: 20, note: 'Bälle', type: { name: 'expense' } },
         ],
       }) as any,
       '2026-08-01',
@@ -297,6 +306,19 @@ describe('buildPdf', () => {
     const buffer = await buildPdf({ name: 'Team A' } as any, [], [], '2026-08-01', '2026-08-31');
 
     expect(buffer.subarray(0, 5).toString('utf-8')).toBe('%PDF-');
+    expect(pdfPageCount(buffer)).toBe(1);
+  });
+
+  it('does not append blank trailing pages when content fits on a single page', async () => {
+    const buffer = await buildPdf(
+      { name: 'Team A' } as any,
+      [cashRow],
+      [receivableRow],
+      '2026-08-01',
+      '2026-08-31',
+    );
+
+    expect(pdfPageCount(buffer)).toBe(1);
   });
 
   it('paginates correctly and stays a valid PDF for many rows', async () => {

myteamwallet_backend/src/cashbox-export/cashbox-export.utils.ts

@@ -26,12 +26,13 @@ export function buildRows(team: Team, from: string, to: string): CashboxExportRo
 
   for (const transaction of team.transactions ?? []) {
     if (!transaction.type) continue;
+    const amount = Number(transaction.amount);
     raw.push({
       date: transaction.date,
       type: transaction.type.name,
       who: 'Teamkasse',
       note: transaction.note,
-      amount: Number(transaction.amount),
+      amount: transaction.type.name === 'expense' ? -amount : amount,
     });
   }
 
@@ -318,6 +319,7 @@ function addFooters(doc: PDFKit.PDFDocument, teamName: string): void {
       .fillColor(COLORS.footerText)
       .text(`${teamName} – Kassenbuch-Report, erstellt am ${generatedAt}`, PAGE_MARGIN, footerY, {
         width: doc.page.width - PAGE_MARGIN * 2 - 60,
+        height: 20,
         lineBreak: false,
       });
     doc
@@ -325,6 +327,7 @@ function addFooters(doc: PDFKit.PDFDocument, teamName: string): void {
       .fillColor(COLORS.footerText)
       .text(`Seite ${i - range.start + 1} von ${range.count}`, doc.page.width - PAGE_MARGIN - 60, footerY, {
         width: 60,
+        height: 20,
         align: 'right',
         lineBreak: false,
       });