MS-258/feat: add sale session export functionality
- Add startSaleSessionExport, getSaleSessionExportFileAudits, and downloadSaleSessionExportFile API functions in saleSession.ts
- Add export endpoint URLs to salleSession config in server.ts (exportSaleSession, getSaleSessionExportFileAudits, downloadSaleSessionExport)
- Add "Sessions de vente" tab in exportMainView with SaleSessionExportListView
- Refactor All-SalesSessionView export: replace client-side CSV export dialog (ExportSaleSessions.tsx) with server-side async export via startSaleSessionExport
- Remove ExportSaleSessions.tsx (client-side batch processing with papaparse)
- Replace export Button with LoadingButton showing export progress state
Closes MS-258