task(E5): CSV seat list export

frontend/src/services/seatingService.ts

@@ -425,6 +425,23 @@ export class SeatingService {
     return { total, byRow, byBlock };
   }
 
+  /**
+   * Task E5: Exportiert eine Sitzplatzliste als CSV-String.
+   * Spalten: Typ, rowId, blockId, X, Y
+   * Zeilentrenner: \n (kompatibel mit Excel via „Daten importieren“).
+   */
+  exportSeatListCSV(elements: CADElement[]): string {
+    const header = 'type,row_id,block_id,x,y';
+    const rows: string[] = [header];
+    for (const el of elements) {
+      if (el.type !== 'chair') continue;
+      const rowId = (el.properties.rowId as string | undefined) ?? '';
+      const blockId = (el.properties.blockId as string | undefined) ?? '';
+      rows.push(`chair,${rowId},${blockId},${el.x.toFixed(1)},${el.y.toFixed(1)}`);
+    }
+    return rows.join('\n');
+  }
+
   /** Get all chairs belonging to a specific row */
   getRowElements(elements: CADElement[], rowId: string): CADElement[] {
     return elements.filter(el => el.type === 'chair' && el.properties.rowId === rowId);