perf: add database indexes, implement caching, enforce permission guards, and sanitize external URLs

paperless-backend/src/email-download/email-download.controller.ts

@@ -11,6 +11,7 @@ export class EmailDownloadController {
 
   @Post('fetch')
   @HttpCode(HttpStatus.OK)
+  @RequirePermissions(Permission.VIEW_MAIL)
   async triggerFetch() {
     this.logger.log('Manueller E-Mail-Abruf wurde ausgelöst.');
     await this.emailDownloadService.handleCron();