Fix: Comprehensive updates for demo organization, subscriptions, and multi-tenancy

- Fixed landing page content with accurate feature descriptions from docs
- Updated subscription banner component to use correct props
- Fixed demo organization seeder issues:
  * Set organization_id for admin and sample users in DatabaseSeeder
  * Changed firstOrCreate to updateOrCreate in MultitenancyDataSeeder
  * Added onboarding_step and onboarding_completed_at fields
  * Marked all demo users as verified with first_login_completed
- Fixed null organization_id errors in controllers:
  * PayrollSettingsController - added organization checks
  * LoanSettingsController - added organization checks
  * EmployeeLoanController - added organization checks for my-loans routes
- Fixed AuditLog scopeForOrganization to handle nullable organization_id
- Restricted subscription and payment routes to org_admin role only
- Updated sidebar to show subscription/payment links only to org_admins
- Updated DemoSubscriptionSeeder to use existing organizations only
- All demo users now properly verified and can access application features
