fix: pagination service, common imports, and build errors

[Jayrodri088]

Summary

Fixes pagination for courses/lessons and resolves backend build errors (wrong imports, missing entity, and dependency/type issues).

Changes

Pagination

• PaginationService (common/services/pagination.service.ts): Implement generic paginate<T>(repository, options, findOptions?) using TypeORM findAndCount, returning { data, total, page, limit, totalPages }.
• PaginationDto (common/dto/pagination.dto.ts): Add query DTO with page (default 1, min 1) and limit (default 10, min 1, max 100), using @Type(() => Number) and class-validator.
• CommonModule: New global module that provides and exports PaginationService; registered in AppModule.
• Courses: GET /courses now accepts ?page=&limit= and returns paginated payload via findAllPaginated; removed duplicate commented GET handler; controller no longer injects PaginationService (used in service).
• Lessons: GET /lessons and GET /lessons/course/:courseId accept ?page=&limit= and return paginated results via findAllPaginated and findAllByCoursePaginated.

Build / codebase fixes

• Imports: Correct paths for User and UserRole (e.g. ../../users/entities/user.entity), Lesson (e.g. ../../lessons/entities/lesson.entity or ./entities/lesson.entity), and UserService (../../users/users.service) in auth, common, courses, lessons, quizzes, and rewards.
• @nestjs/mapped-types: Version set to ^2.0.2 in package.json so PartialType resolves and Update DTOs type-check.
• Progress entity: Replace empty stub with TypeORM entity (id, completed, user/userId, lesson/lessonId) so ProgressService compiles and runs.
• Quizzes: Add QuestionType import from ../entities/question.entity in quiz-response.dto.ts.
• Certificates: Use UserRole.ADMIN instead of 'admin' in @Roles() for admin-only routes.

Testing

• npm run build passes (exit code 0).
• GET /courses and GET /lessons (and GET /lessons/course/:courseId) support ?page=1&limit=10 and return paginated responses without runtime errors.

Closes: #156