Integrate Supabase for authentication and data management

• Added .env.example for environment variable configuration.
• Updated .gitignore to exclude .env files.
• Refactored index.html for improved structure.
• Added Supabase dependencies in package.json and package-lock.json.
• Created supabase.js for Supabase client initialization.
• Implemented authentication flow in auth.js with sign-in and sign-up functionality.
• Developed dashboard.js to display user-specific content after authentication.
• Created home.js for the landing page with navigation to the auth page.
• Enhanced styling in style.css for a better user interface.
• Added NASA logo SVG asset for branding.