Cleanup:
- Deleted 5 unused flows (enrollment-inviation, headscale-auth/authz, default-enrollment, oauth-enrollment)
- Deleted 8 orphaned stages bound only to deleted flows
- Deleted authentik Read-only group and role (0 users)
- Deleted 2 unbound policies (map github username, Map Google Attributes)
Invitation enrollment:
- Created invitation-enrollment flow with 5 stages (invitation validation,
identification with social login, prompt, user write, auto-login)
- Set all OAuth sources (Google/GitHub/Facebook) enrollment_flow to invitation-enrollment
- New users can only sign up via single-use invitation links
- Added authentik-invite.sh script for invitation management
- Updated reference docs and authentik skill
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