Fix Authentication Issues and Add Admin Link

[virtuehearts]

This PR addresses three main issues:

1. Google OAuth "Unable to connect" error: Fixed by removing the hardcoded NEXTAUTH_URL in the environment initialization. This allows NextAuth to automatically detect the correct host and port, which is crucial when the app is running on a port other than 3000 or behind a proxy/tunnel.
2. Admin/Returning User login errors: Implemented email normalization (lowercase) throughout the authentication and registration flows. This ensures that users can log in regardless of the casing they used during registration or in the admin environment variables.
3. Admin Accessibility: Added a subtle "Admin Sanctuary" link to the landing page footer to provide a direct path to the admin panel.

All changes have been verified with linting, database tests, and manual frontend verification using Playwright.

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PR created automatically by Jules for task 11649122699819831769 started by @virtuehearts

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