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

fix(question-bank): make batch status updates safe and efficient

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

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

fix(database): normalize FK column types for refactored schema sync

refactor: resolve circular dependencies and optimize entities for SWC builder

feat: enhance Swagger documentation with examples and descriptions

fix: align entities with DB schema - files, folders, rubrics

added swagger feature and fixed some errors in the "files" feature

Phase 3 updates before merging into enrollments