Add StudentQuestion and StudentQuestionMessage models

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

prisma/schema.prisma

@@ -37,6 +37,9 @@ model User {
   accessLogs           AccessLog[] @relation("AccessLogUser")
   adminAccessLogs      AccessLog[] @relation("AccessLogAdmin")
   balanceTransactions  BalanceTransaction[]
+  questions            StudentQuestion[]
+  closedQuestions      StudentQuestion[]       @relation("QuestionClosedBy")
+  questionMessages     StudentQuestionMessage[]
 }
 
 model Session {
@@ -111,6 +114,7 @@ model Course {
   modules     Module[]
   enrollments CourseEnrollment[]
   accessLogs  AccessLog[]
+  questions   StudentQuestion[]
 }
 
 model Module {
@@ -312,6 +316,45 @@ model LessonComment {
   replies LessonComment[] @relation("CommentReplies")
 }
 
+// ─────────────────────────────────────────────
+// Student Questions
+// ─────────────────────────────────────────────
+
+enum QuestionStatus {
+  OPEN
+  CLOSED
+}
+
+model StudentQuestion {
+  id         String         @id @default(cuid())
+  userId     String
+  courseId   String?
+  title      String
+  status     QuestionStatus @default(OPEN)
+  closedAt   DateTime?
+  closedById String?
+  createdAt  DateTime       @default(now())
+  updatedAt  DateTime       @updatedAt
+
+  user      User                     @relation(fields: [userId], references: [id], onDelete: Cascade)
+  course    Course?                  @relation(fields: [courseId], references: [id], onDelete: SetNull)
+  closedBy  User?                    @relation("QuestionClosedBy", fields: [closedById], references: [id], onDelete: SetNull)
+  messages  StudentQuestionMessage[]
+}
+
+model StudentQuestionMessage {
+  id         String   @id @default(cuid())
+  questionId String
+  authorId   String
+  text       String
+  files      Json?    // [{name, url, size}]
+  isRead     Boolean  @default(false)
+  createdAt  DateTime @default(now())
+
+  question StudentQuestion @relation(fields: [questionId], references: [id], onDelete: Cascade)
+  author   User            @relation(fields: [authorId], references: [id], onDelete: Cascade)
+}
+
 // ─────────────────────────────────────────────
 // Balance
 // ─────────────────────────────────────────────