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.controller.ts

@@ -0,0 +1,27 @@
+import { Controller, Get, Post, Param, Body } from '@nestjs/common';
+import { ApiTags, ApiBearerAuth } from '@nestjs/swagger';
+import { ModerationService } from './moderation.service';
+import { CurrentUser } from '../auth/decorators/current-user.decorator';
+import { User } from '@coursecraft/database';
+
+@ApiTags('moderation')
+@Controller('moderation')
+@ApiBearerAuth()
+export class ModerationController {
+  constructor(private moderationService: ModerationService) {}
+
+  @Get('pending')
+  async getPendingCourses(@CurrentUser() user: User): Promise<any> {
+    return this.moderationService.getPendingCourses(user.id);
+  }
+
+  @Post(':courseId/approve')
+  async approveCourse(@Param('courseId') courseId: string, @Body('note') note: string, @CurrentUser() user: User): Promise<any> {
+    return this.moderationService.approveCourse(user.id, courseId, note);
+  }
+
+  @Post(':courseId/reject')
+  async rejectCourse(@Param('courseId') courseId: string, @Body('reason') reason: string, @CurrentUser() user: User): Promise<any> {
+    return this.moderationService.rejectCourse(user.id, courseId, reason);
+  }
+}