Feat/organization management (#43)

* initial push

* build fix

* more informative error message

* Add authentication and organization handling to bulk experiment creation

* feat: add comprehensive organization management system

- Add full organization member management UI with role-based permissions
- Implement invite system with email invitations and role assignment
- Add member role management (Owner, Admin, Member, Viewer)
- Implement leave organization and delete organization features
- Create API endpoints for all organization operations
- Integrate with Stack Auth teams for authentication
- Add proper permission checks for all sensitive operations
- Display pending invitations with cancel functionality
- Fix critical bugs: toast delay (1000s->5s), console.log cleanup, CSS theme colors
- Add null safety checks throughout Stack Auth integrations
- Update organization settings page with new member management tab

* fix: replace global admin checks with organization-based permissions

Users who create their own organizations can now:
- Create Prolific studies for their experiments
- View and manage Prolific study details
- Sync Prolific data
- Create video comparison tasks

Changed requireAdmin() to check organization membership/ownership instead of global admin status.

Update README.md

Create SECURITY.md