Move SchoolDashboard out of RoleDashboards.tsx #137

What this is for

RoleDashboards.tsx is a 3,100+ line file holding all 8 role dashboards. We're moving each one into its own file so the codebase is easier to navigate. This is the smallest dashboard — good place to start.

What to move

export const SchoolDashboard (~96 lines) — the dashboard shown to School/Principal-role users.

Steps

1. Create frontend/src/components/dashboards/SchoolDashboard.tsx.
2. Cut the SchoolDashboard component out of RoleDashboards.tsx and paste it into the new file.
3. Add whatever imports it needs at the top (React, any icons/types it uses — copy the relevant ones from the top of RoleDashboards.tsx).
4. Keep the export const SchoolDashboard = ... exactly as it was.
5. Back in RoleDashboards.tsx, where the component used to be, add: export { SchoolDashboard } from './dashboards/SchoolDashboard'; — this way App.tsx doesn't need any changes.
6. Don't change any logic or JSX — copy it exactly as-is.

How to check your work

1. cd frontend && npm run lint — no errors.
2. npm run build — succeeds.
3. Run npm run dev, log in as a School/Principal user, and confirm the dashboard looks and behaves exactly the same as before.

Part of #136.