feat: frontend tests for platform/ forms and pages

[Copilot]

No frontend tests existed for any of the platform/ components. This adds 18 test files covering all major forms, dialogs, and page-level components.

New tests (frontend/src/test/platform/)

Dialogs & confirmation forms

• DeleteContentForm, DeleteCoursePopup, DeleteUserDialog — confirmation message interpolation, cancel/delete callbacks, API integration
• EnableCourseSwitchPopup — enable/disable title variants, confirm flow

Data-entry forms

• OrganizationForm — create/edit modes, required-field and URL validation, success callback
• UserForm — add/edit modes, role descriptions, instructor display-name validation (whitespace-only bypass of HTML required)
• CreateImapForm — field validation, folder chip add/remove, submit
• CreateInstructorForm — email/display-name validation, submit
• EnrollMenu — dropdown open, manual enrollment dialog, email validation, success flow

Composite components

• AddImapConnectionForm — no-connection accordion vs. existing-connection select
• AddInstructorsSection — no-instructor accordion, instructor select label, pre-selection chips
• ContentTable — fetch-loaded rows, delete and click events dispatched via eventHandler
• QuestionForm — viewer vs. editor role gating, delete event, options table

Enrollment & pages

• EnrollmentList — empty state, row rendering, row click
• Courses, Organizations, ApiKeys — full page render via Base/MenuBar with fetch mocks, role-gated buttons, dialogs

Source changes

Courses.jsx, Organizations.jsx, and ApiKeys.jsx are Django-template entry points that define a component and immediately call render({children: <Component />}) with no export. Added export default to each so tests can import the component directly — the runtime behavior is unchanged.

// Before
render({children: <Courses />});

// After
export default Courses;
render({children: <Courses />});