Backend changes:
- Removed authentication requirement from GET /api/users/:username endpoint
- Removed authentication requirement from GET /api/users/:username/ratings endpoint
- These are public profile endpoints and should be accessible to all users
Frontend changes:
- PublicProfilePage now shows NotFoundPage component when user doesn't exist
- Unified 404 behavior: both invalid URLs and non-existent users show the same 404 page
- NotFoundPage "Requested URL" box now only shows in dev mode (import.meta.env.DEV)
- Removed unused AlertCircle icon import from PublicProfilePage
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