chore(import): improve error handling and add flyer integration

- Replace BadRequestException with UnauthorizedException for authentication failures in flyer-import and flyer-selection controllers
- Add bulk selection endpoint in FlyerSelectionController for creating multiple selections in one request
- Update FlyerSelectionModule to include new FlyerSelectionMatcherService and FlyerSelectionSyncController
- Extend FlyerSelectionService with createMany method for bulk operations
- Add new DTOs for bulk selection and receipt matching functionality
- Update ReceiptImportService to accept FlyerSelectionService dependency and track successful rows
- Extend SaveReceiptResponse with flyerAutoSync field for receipt-to-flyer matching results
- Add new API paths for flyer import and selection endpoints
- Update Flutter UI to include Flyer import tab and adjust tab controller length
- Add new domain models and repository methods for flyer import functionality
- Update test files to include new FlyerSelectionService dependency
- Modify .kilo plan documentation to reflect current system architecture

backend/src/flyer-import/flyer-import.controller.ts

@@ -4,6 +4,7 @@ import {
   HttpCode,
   Post,
   Request,
+  UnauthorizedException,
   UploadedFile,
   UseInterceptors,
 } from '@nestjs/common';
@@ -51,7 +52,7 @@ export class FlyerImportController {
           : undefined;
 
     if (!userId) {
-      throw new BadRequestException('Kunde inte identifiera användaren.');
+      throw new UnauthorizedException('Kunde inte identifiera användaren.');
     }
 
     return this.flyerImportService.parseAndMatch(file, userId);