feat(exams): add exam record deletion and accurate list counts

fix(files): return 404 when file missing on disk; polish Word/PDF export

feat(exams): improve export media handling and register client PDFs

fix(backend): return previewable group media URLs in question and exam APIs

feat(exams): generate real DOCX paper exports and align export layout

feat(assessment): implement Question Bank and Exam Generator backend

feat: add exam drafts functionality with pagination and image upload support in question bank

feat: add exam drafts functionality with pagination and image upload support in question bank

feat: implement question bank and exam modules with associated services, controllers, and entities