Add homework review workflow: statuses, audio, file attachments, tabs

- HomeworkSubmission: add status (PENDING/REVIEWING/APPROVED/REJECTED) + statusAt
- HomeworkFeedback: add files (Json) + audioUrl fields
- Curator detail page: meta table, content tabs, feedback history with audio/files
- FeedbackForm: file upload, audio recorder (Web Audio API + S3), action buttons
- AudioRecorder component: record → preview → upload to S3
- ContentTabs: toggle between homework description and lesson content (TipTap read-only)
- Homework list: 4-color status badges with proper filtering
- API routes: /api/curator/upload and /api/curator/audio-upload

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/curator/dashboard/page.tsx

@@ -13,7 +13,7 @@ export default async function CuratorDashboard() {
     prisma.homeworkSubmission.count(),
     prisma.homeworkFeedback.count({
       where: {
-        createdAt: { gte: new Date(Date.now() - 7 * 24 * 60 * 60 * 1000) },
+        createdAt: { gte: new Date(new Date().getTime() - 7 * 24 * 60 * 60 * 1000) },
         curatorId: session.user.id,
       },
     }),