Enhance Loader Animation for Better User Feedback

**Current Problem:**
The existing loader animation does not clearly indicate when a process (e.g., fetching data, uploading files, or generating questions) is in progress. As a result, users may be confused about whether an operation is still running or has failed. The lack of smooth and visible feedback affects the user experience.

**Proposed Solution:**
Improve the existing loader by adding a clear and user-friendly spinner animation.
Ensure the loader is prominently visible while the process is running.
Prevent user interaction during loading to avoid duplicate requests.
Add a fade-in/fade-out transition to make the experience smoother.

**Steps to Reproduce (Before Fix):**
Click on the "Next" button or upload a file.
The loader does not display properly, causing confusion about whether the process is still running.

**Expected Behavior (After Fix):**
A visible and smooth spinner appears while an operation is in progress.
The UI is disabled until loading completes, preventing duplicate actions.
The loader smoothly disappears when the process is finished.