feat: add certificates, groups, support system, and moderation

Backend changes:
- Add Certificate generation service with beautiful HTML templates
- Add CourseGroup, GroupMember, GroupMessage models for group collaboration
- Add Homework and HomeworkSubmission models with AI + teacher grading
- Add SupportTicket and TicketMessage models for help desk
- Add Moderation API for admin/moderator course approval workflow
- All new modules: CertificatesModule, GroupsModule, SupportModule, ModerationModule

Frontend changes:
- Add certificate download button when course completed
- Update course page to load enrollment progress from backend
- Integrate lesson completion with backend API

Database schema now supports:
- Course groups with chat functionality
- Homework assignments with dual AI/human grading
- Support ticket system with admin responses
- Full moderation workflow (PENDING_REVIEW -> PUBLISHED/REJECTED)

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/moderation/moderation.module.ts

@@ -0,0 +1,10 @@
+import { Module } from '@nestjs/common';
+import { ModerationController } from './moderation.controller';
+import { ModerationService } from './moderation.service';
+
+@Module({
+  controllers: [ModerationController],
+  providers: [ModerationService],
+  exports: [ModerationService],
+})
+export class ModerationModule {}