Adds Google OAuth alongside existing Apple and email/password auth. Follows the same patterns as Apple Sign-In: state cookie for CSRF, anonymousId migration, and user linking by email. Key differences: Google callback is a GET redirect (sameSite: lax) and uses a static client secret instead of a signed JWT.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- Fix AuthModal to pass anonymousId on both signin and signup
- Add comprehensive migration logic in signin that moves anonymous completion stats to authenticated user
- Implement deduplication algorithm to handle overlapping completion dates
- Maintain earliest completion when duplicates exist
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Co-Authored-By: Claude <noreply@anthropic.com>
George Powell