Replace Loading Spinner with Skeleton UI Across Mentorship Portal

Currently, pages in the mentorship portal (both internal and public) show a traditional loading spinner while data is being fetched.

To improve user experience and reduce perceived loading time, we want to replace all loading spinners with **skeleton screens** that mimic the structure of the content being loaded.

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### **Requirements**
- Replace all loading spinners with skeleton UI components across the portal:
- Internal pages (admin/mentor view under `/my/mentorship/`)
- Public pages (program and module views under `/mentorship`)
- Skeletons should reflect the layout and structure of each page (e.g., cards, tables, lists).
- Ensure skeletons display only while data is loading, and disappear once data is available.
- Maintain accessibility standards (e.g., appropriate ARIA roles).
- Keep responsiveness intact (skeletons should work on mobile and desktop layouts).