feat(admin): add Courses Without BR page (#142)

[mohitmohan2005-wq]

Closes #142
Adds an admin page listing courses that have no branch representative assigned, backed by the getCoursesWithoutBR endpoint.

• fetchCoursesWithoutBR in admin/src/apis/br.js
• CoursesWithoutBR page + coursesWithoutBRTable component
• Wire up /admin/courses-without-br route and sidebar nav item

[DreamBot706]

Review Summary:
The implementation of the new page and routing works, but there are security and performance issues that need fixing before this can be merged. We also need to stick to the established naming conventions. Address the inline comments below.

File Comments:

• File: admin/src/apis/br.js

  • Comment: Security: You are using a hardcoded token (Bearer admin-coursehub-cc23-golang) in the Authorization header. Fetch this dynamically from environment variables or secure storage (like localStorage), similar to how authentication is handled in other API functions. Never hardcode tokens.

• File: admin/src/components/coursesWithoutBRTable.jsx

  • Comment: Convention: Rename this file to PascalCase (CoursesWithoutBRTable.jsx) to match the naming convention of all other React components in this project.
  • Comment: UX: If the courses array is empty, the table renders headers but no rows. Implement a proper empty state (e.g., a "No courses found" message) when courses.length === 0.

• File: server/modules/br/br.controller.js (Function: getCoursesWithoutBR)

  • Comment: Performance: This function fetches all users, all BR records, and all courses into application memory before filtering them in JavaScript. This will not scale. Refactor this to use MongoDB aggregation ($lookup and $match) so the filtering is done at the database level.