feat: add recommended courses and quiz multiple attempts

- Add is_recommended field to Course model
- Add allow_multiple_attempts field to Quiz model
- Create RecommendedCoursesController for admin management
  - List all approved courses
  - Get course by ID
  - Toggle recommendation status
- Add is_recommended filter to CoursesService.ListCourses
- Add allow_multiple_attempts to quiz update and response types
- Update ChaptersLessonService.updateQuiz to support allow_multiple_attempts

.agent/workflows/database-migration.md

@@ -0,0 +1,311 @@
+---
+description: How to create and run database migrations
+---
+
+# Database Migration Workflow
+
+Follow these steps to create and apply database migrations using Prisma.
+
+---
+
+## Step 1: Update Prisma Schema
+
+Edit `prisma/schema.prisma`:
+
+```prisma
+model Course {
+  id              Int      @id @default(autoincrement())
+  title           Json     // { th: "", en: "" }
+  description     Json
+  price           Decimal  @db.Decimal(10, 2)
+  is_free         Boolean  @default(false)
+  have_certificate Boolean @default(false)
+  status          CourseStatus @default(DRAFT)
+  thumbnail       String?
+  
+  category_id     Int
+  category        Category @relation(fields: [category_id], references: [id])
+  
+  created_by      Int
+  creator         User     @relation(fields: [created_by], references: [id])
+  
+  chapters        Chapter[]
+  instructors     CourseInstructor[]
+  enrollments     Enrollment[]
+  
+  created_at      DateTime @default(now())
+  updated_at      DateTime @updatedAt
+  deleted_at      DateTime?
+  is_deleted      Boolean  @default(false)
+  
+  @@index([category_id])
+  @@index([status])
+  @@index([is_deleted])
+}
+```
+
+---
+
+## Step 2: Create Migration
+
+// turbo
+Run migration command:
+```bash
+npx prisma migrate dev --name add_course_model
+```
+
+This will:
+1. Generate SQL migration file
+2. Apply migration to database
+3. Regenerate Prisma Client
+
+---
+
+## Step 3: Review Migration File
+
+Check generated SQL in `prisma/migrations/`:
+
+```sql
+-- CreateTable
+CREATE TABLE "Course" (
+    "id" SERIAL NOT NULL,
+    "title" JSONB NOT NULL,
+    "description" JSONB NOT NULL,
+    "price" DECIMAL(10,2) NOT NULL,
+    "is_free" BOOLEAN NOT NULL DEFAULT false,
+    ...
+    CONSTRAINT "Course_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "Course_category_id_idx" ON "Course"("category_id");
+```
+
+---
+
+## Step 4: Update Prisma Client
+
+// turbo
+Regenerate client if needed:
+```bash
+npx prisma generate
+```
+
+---
+
+## Step 5: Create Seed Data (Optional)
+
+Update `prisma/seed.js`:
+
+```javascript
+const { PrismaClient } = require('@prisma/client');
+const prisma = new PrismaClient();
+
+async function main() {
+  // Create categories
+  const category = await prisma.category.create({
+    data: {
+      name: { th: 'การเขียนโปรแกรม', en: 'Programming' },
+      description: { th: 'หลักสูตรด้านการเขียนโปรแกรม', en: 'Programming courses' }
+    }
+  });
+
+  // Create test user
+  const user = await prisma.user.create({
+    data: {
+      username: 'instructor1',
+      email: 'instructor@example.com',
+      password: '$2b$10$...', // hashed password
+      role_id: 2 // INSTRUCTOR
+    }
+  });
+
+  // Create test course
+  const course = await prisma.course.create({
+    data: {
+      title: { th: 'Python สำหรับผู้เริ่มต้น', en: 'Python for Beginners' },
+      description: { th: 'เรียนรู้ Python', en: 'Learn Python' },
+      price: 990,
+      is_free: false,
+      category_id: category.id,
+      created_by: user.id
+    }
+  });
+
+  console.log('Seed data created:', { category, user, course });
+}
+
+main()
+  .catch((e) => {
+    console.error(e);
+    process.exit(1);
+  })
+  .finally(async () => {
+    await prisma.$disconnect();
+  });
+```
+
+---
+
+## Step 6: Run Seed
+
+// turbo
+Seed the database:
+```bash
+npx prisma db seed
+```
+
+---
+
+## Common Migration Tasks
+
+### Add New Field
+```prisma
+model Course {
+  // ... existing fields
+  slug String @unique  // New field
+}
+```
+
+// turbo
+```bash
+npx prisma migrate dev --name add_course_slug
+```
+
+### Add Index
+```prisma
+model Course {
+  // ... existing fields
+  
+  @@index([created_at])  // New index
+}
+```
+
+### Add Relation
+```prisma
+model Lesson {
+  // ... existing fields
+  
+  quiz_id Int?
+  quiz    Quiz? @relation(fields: [quiz_id], references: [id])
+}
+```
+
+### Rename Field
+```prisma
+model Course {
+  // Old: instructor_id
+  created_by Int  // New name
+}
+```
+
+**Note**: Prisma will detect rename and ask for confirmation
+
+---
+
+## Production Migration
+
+### Step 1: Generate Migration (Dev)
+```bash
+npx prisma migrate dev --name migration_name
+```
+
+### Step 2: Commit Migration Files
+```bash
+git add prisma/migrations/
+git commit -m "Add migration: migration_name"
+```
+
+### Step 3: Deploy to Production
+```bash
+npx prisma migrate deploy
+```
+
+**Important**: Never use `migrate dev` in production!
+
+---
+
+## Rollback Migration
+
+### Option 1: Manual Rollback
+```bash
+# Find migration to rollback
+ls prisma/migrations/
+
+# Manually run the down migration (if exists)
+psql $DATABASE_URL < prisma/migrations/XXXXXX_migration_name/down.sql
+```
+
+### Option 2: Reset Database (Dev Only)
+```bash
+npx prisma migrate reset
+```
+
+**Warning**: This will delete all data!
+
+---
+
+## Troubleshooting
+
+### Migration Failed
+```bash
+# Check database status
+npx prisma migrate status
+
+# Resolve migration
+npx prisma migrate resolve --applied MIGRATION_NAME
+# or
+npx prisma migrate resolve --rolled-back MIGRATION_NAME
+```
+
+### Schema Drift
+```bash
+# Check for drift
+npx prisma migrate diff
+
+# Reset and reapply
+npx prisma migrate reset
+```
+
+### Generate Client Error
+```bash
+# Clear node_modules and reinstall
+rm -rf node_modules
+npm install
+
+# Regenerate client
+npx prisma generate
+```
+
+---
+
+## Checklist
+
+- [ ] Schema updated in `prisma/schema.prisma`
+- [ ] Migration created with descriptive name
+- [ ] Migration SQL reviewed
+- [ ] Migration applied successfully
+- [ ] Prisma Client regenerated
+- [ ] Seed data updated (if needed)
+- [ ] Tests updated for new schema
+- [ ] Migration files committed to git
+
+---
+
+## Best Practices
+
+1. **Descriptive Names**: Use clear migration names
+   - ✅ `add_course_certificate_field`
+   - ❌ `update_schema`
+
+2. **Small Migrations**: One logical change per migration
+
+3. **Review SQL**: Always check generated SQL before applying
+
+4. **Test First**: Test migrations on dev database first
+
+5. **Backup**: Backup production database before migrating
+
+6. **Indexes**: Add indexes for frequently queried fields
+
+7. **Constraints**: Use database constraints for data integrity