Implement configurable platform + tenant onboarding builder

[RavenLLevitt]

Summary

• Add a configurable onboarding system with two levels:
  • Platform-level defaults (including signup-option-specific variants)
  • Tenant-level onboarding steps managed from Root Dashboard
• Add default seeded platform steps for name and picture.
• Add tenant template steps for:
  • Follow organizations
  • Add friends
• Replace the old static onboarding wizard with a dynamic flow renderer that resolves steps from platform + tenant config and submits responses.
• Apply template effects during onboarding submit (org follow + friend request creation).

Backend

• Added onboarding config service with normalization/sanitization/resolution logic.
• Extended global config with platform onboarding storage.
• Added tenant onboarding config model in tenant DB.
• Added/updated APIs:
  • GET /admin/platform-onboarding-config
  • PUT /admin/platform-onboarding-config
  • GET /admin/tenant-onboarding-template-library
  • GET /admin/tenant-onboarding-config
  • PUT /admin/tenant-onboarding-config
  • GET /onboarding-config
  • GET /onboarding-profile (org/user search for template steps)
  • POST /submit-onboarding
• Added onboarding response fields to user schema.

Frontend

• Added reusable visual builder component: OnboardingBuilder.
• Added platform onboarding builder to Admin → Platform Admins page.
• Added tenant onboarding page under Root Dashboard.
• Added shortcut card in Root dashboard landing panel.
• Replaced /onboard page with dynamic onboarding step runner supporting:
  • text, textarea, number
  • single/multi-select
  • picture upload
  • follow orgs/add friends template steps

Validation

• Frontend build succeeds after changes.
• Targeted backend route-outcome tests pass for auth/user routes.

Notes

• Existing repository-wide frontend lint warnings remain (pre-existing), but changes compile and targeted tests pass.