feature: Pin course in the courses page

[shubhamku044]

Is your feature request related to a problem? Please describe. I have multiple courses from previous cohort and this cohort, so when I want to view my course I need to scroll down to the bottom Describe the solution you'd like Just like instagram we pin posts and that post is visible at the top, can we also do the same here

[himanshukandari14]

To solve this issue, I'll add a isPinned field in the database, update the API to sort pinned courses first, and create an endpoint to toggle the pin status. On the frontend, I'll add a "Pin" button to update the status and ensure pinned courses are displayed at the top of the courses page.