feat(roster): implement class roster management and submission validation

prisma/schema.prisma

@@ -1,5 +1,6 @@
 generator client {
   provider = "prisma-client-js"
+  output   = "../src/generated/prisma"
 }
 
 datasource db {
@@ -29,6 +30,7 @@ model Class {
   teacherId   String
   course      Course       @relation(fields: [courseId], references: [id], onDelete: Cascade)
   assignments Assignment[]
+  students    ClassStudent[]
   createdAt   DateTime     @default(now())
   updatedAt   DateTime     @updatedAt
 
@@ -73,3 +75,15 @@ model Submission {
 
   @@unique([assignmentId, studentId])
 }
+
+model ClassStudent {
+  id           Int      @id @default(autoincrement())
+  classroomId  Int
+  studentId    String
+  studentName  String
+  createdAt    DateTime @default(now())
+  updatedAt    DateTime @updatedAt
+  classroom    Class    @relation(fields: [classroomId], references: [id], onDelete: Cascade)
+
+  @@unique([classroomId, studentId])
+}