P0-1/P0-2/P1-1: dimensions form + E2E tests + PDF export

P0-1 Backend: dimensions column on template entity + validation
P0-1 Frontend: dimensions edit UI in TemplateManager
P0-2: routeAfterGrading unit tests (10 cases), service spec fix + certificate tests, jest-e2e.json
P1-1: proper PDF generation with embedded CJK font via pdf-lib low-level API

server/src/assessment/assessment.controller.ts

@@ -271,12 +271,12 @@ export class AssessmentController {
   }
 
   @Get(':id/export/pdf')
-  @ApiOperation({ summary: 'Export assessment to PDF (text format)' })
+  @ApiOperation({ summary: 'Export assessment to PDF' })
   async exportPdf(@Param('id') sessionId: string) {
     const buffer = await this.exportService.exportToPdf(sessionId);
     return {
-      filename: `assessment-${sessionId}.txt`,
-      content: buffer.toString('utf-8'),
+      filename: `assessment-${sessionId}.pdf`,
+      buffer: buffer.toString('base64'),
     };
   }
 }