task(E5): CSV seat list export

frontend/tests/seating.count.test.ts

@@ -82,3 +82,29 @@ describe('countSeats', () => {
     expect(Object.keys(result.byRow).length).toBe(1);
   });
 });
+
+describe('exportSeatListCSV', () => {
+  const svc = new SeatingService();
+
+  it('erzeugt CSV mit Header und Stuhl-Zeilen', () => {
+    const els = svc.createSeatingRow(0, 0, 'layer-1', { count: 3 });
+    const csv = svc.exportSeatListCSV(els);
+    const lines = csv.split('\n');
+    expect(lines[0]).toBe('type,row_id,block_id,x,y');
+    expect(lines.length).toBe(4); // Header + 3 Stühle
+    expect(lines[1]).toContain('chair');
+  });
+
+  it('ignoriert Nicht-Stuhl-Elemente', () => {
+    const chairs = svc.createSeatingRow(0, 0, 'layer-1', { count: 2 });
+    const other: CADElement = {
+      id: 'x1', type: 'rect', layerId: 'l', x: 0, y: 0, width: 1, height: 1, properties: {},
+    } as unknown as CADElement;
+    const csv = svc.exportSeatListCSV([...chairs, other]);
+    expect(csv.split('\n').length).toBe(3); // Header + 2 Stühle
+  });
+
+  it('leere Eingabe ergibt nur Header', () => {
+    expect(svc.exportSeatListCSV([])).toBe('type,row_id,block_id,x,y');
+  });
+});