Improve exam flow, enhance conversation log UI, and fix session questions saving

[jordan-jakisa]

This pull request introduces several improvements to both the backend and frontend, focusing on better user experience, UI polish, and streamlined exam flow. The key changes include enhanced exam material handling, improved conversation log display, and a more intuitive process for starting exams after question generation.

Exam material and exam flow improvements:

• Materials are now sorted by upload time in descending order when loaded, ensuring the most recent materials appear first (ExamContext.tsx).
• When starting an exam, the app checks if the selected material has questions. If not, it automatically triggers question generation and then starts the exam once questions are ready (UploadPage.tsx). [1] [2]
• State cleanup is improved after question generation and modal closure to prevent unintended exam starts and ensure UI consistency (UploadPage.tsx). [1] [2]

UI and conversation log display enhancements:

• The conversation log modal layout is improved for better responsiveness and readability, including proper handling of long file paths, sticky header/footer, and hiding the close button on small screens (ConversationLogDisplay.tsx). [1] [2]
• The "Saved to" path for the conversation log is now displayed with better word wrapping and alignment for clarity (ExamPage.tsx).

Backend session data handling:

• The backend now updates the answers_data in the session more robustly by creating a new array with the latest answer, ensuring immutability and preventing side effects (exam.py).