fix: loading screen, split tests, semantics, misc fix

[wenhwang97]

Address feedback on 10/23/2024

• Add loading screen as landing page
  • Use Loading as landing page
  • Redirect to /auth if study ID not found in the URL
  • Access /assessments directly will still redirect to /auth
• Refactor react router
• No longer display study ID in URL during the assessment
• Fix semantics
• Create two sets of questions for baseline and followup
• Switch to touch event for Spatial Memory test for smooth animation
• Hide images for rendering before starting the question for Visual Paired test