fix: address cashbox-export whole-branch review findings

- Reject dates that are not strict YYYY-MM-DD (was accepting full ISO
  datetimes, which silently produced empty exports instead of a 400)
  and reject from > to with a 400 before touching the team/DB.
- Emit the cashbox_export_download and cashbox_export_subscription_update
  audit log events that were declared but never fired, matching the
  audit trail every sibling feature already has.
- Restore full type checking on the pdfkit import via `import = require()`
  instead of an untyped require() with an eslint-disable.
- Tighten a cashbox.spec.ts assertion to check the exact dialog class
  instead of expect.anything(), so it can't pass with the wrong dialog
  wired to the Export button.
- Style and announce the export dialogs' error messages using this
  codebase's established error-message/role=alert pattern.

myteamwallet_backend/src/cashbox-export/dto/cashbox-export-query.dto.ts

@@ -1,10 +1,10 @@
-import { IsDateString, IsIn } from 'class-validator';
+import { IsIn, Matches } from 'class-validator';
 
 export class CashboxExportQueryDto {
-  @IsDateString()
+  @Matches(/^\d{4}-\d{2}-\d{2}$/)
   from: string;
 
-  @IsDateString()
+  @Matches(/^\d{4}-\d{2}-\d{2}$/)
   to: string;
 
   @IsIn(['csv', 'pdf'])