feat: add accessible auto-generate clips toggle (#32)

[Emins25]

Summary

• update the create page toggle copy to the requested “Auto-generate clips” language and keep the active state on-brand
• add an accessible switch implementation plus the muted estimated processing-time note
• refresh the create-page test coverage for the new switch semantics and stabilize the existing hidden file-input test

Testing

• npm ci
• npx vitest run app/create/__tests__/page.test.tsx
• npm run build (fails due pre-existing unrelated errors in clips-frontend/app/components/DashboardHeader.tsx, clips-frontend/app/dashboard/layout.tsx, and clips-frontend/app/demo/social-platforms/page.tsx)