* Check for pending invitations before creating new Family during SSO account creation
When a user signs in via Google SSO and doesn't have an account yet, the
system now checks for pending invitations before creating a new Family.
If an invitation exists, the user joins the invited family instead.
- OidcAccountsController: check Invitation.pending in link/create_user
- API AuthController: check pending invitations in sso_create_account
- SessionsController: pass has_pending_invitation to mobile SSO callback
- Web view: show "Accept Invitation" button when invitation exists
- Flutter: show "Accept Invitation" tab/button when invitation pending
https://claude.ai/code/session_019Tr6edJa496V1ErGmsbqFU
* Fix external assistant tests: clear Settings cache to prevent test pollution
The tests relied solely on with_env_overrides to clear configuration, but
rails-settings-cached may retain stale Setting values across tests when
the cache isn't explicitly invalidated. Ensure both ENV vars AND Setting
values are cleared with Setting.clear_cache before assertions.
https://claude.ai/code/session_019Tr6edJa496V1ErGmsbqFU
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Co-authored-by: Claude <noreply@anthropic.com>
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