Persists marketing attribution and registration metadata for new users
across the three signup paths (email, Google, GitHub):
- 5 utm_* columns + registration_ip on the users table
- PreservesUtmParameters trait stores incoming utm_* query params on
the register/redirect GET, retrieves them on the POST/callback —
surviving the OAuth round-trip via session
- request()->ip() captured at the controller layer
Adds GitHub as a second OAuth provider:
- GitHubController mirroring the Google one (now renamed from
SocialLoginController for symmetry)
- Settings → Authentication can connect/disconnect GitHub like Google
- Single SocialLogin.vue component replaces the per-provider buttons
on Login/Register, rendering each enabled provider plus a single
"or continue with" divider
UserFactory gains defaults for the new nullable columns so model
strict-mode access in tests doesn't trip.
