When inviting an email without an InvoiceShelf account, the email now
links to a registration page (/register?invitation={token}) instead of
login. After registering, the invitation is auto-accepted.
Backend:
- InvitationRegistrationController: public details() and register()
endpoints. Registration validates token + email match, creates account,
auto-accepts invitation, returns Sanctum token.
- AuthController: login now accepts optional invitation_token param to
auto-accept invitation for existing users clicking the email link.
- CompanyInvitationMail: conditional URL based on user existence.
- Web route for /invitations/{token}/decline (email decline link).
Frontend:
- RegisterWithInvitation.vue: fetches invitation details, shows company
name + role, registration form with pre-filled email.
- Router: /register route added.
Tests: 3 new tests (invitation details, register + accept, email mismatch).
