feat: auto-populate department_id on create + seed default campus with backfill

apps/server/src/students/dto/student.dto.ts

@@ -1,4 +1,4 @@
-import { IsString, IsOptional, IsEnum, IsNumber } from 'class-validator';
+import { IsString, IsOptional, IsEnum, IsNumber, IsInt } from 'class-validator';
 
 export class CreateStudentDto {
   @IsString()
@@ -39,6 +39,13 @@ export class CreateStudentDto {
   @IsOptional()
   @IsString()
   supervisor?: string;
+  @IsOptional()
+  @IsInt()
+  departmentId?: number;
+
+  @IsOptional()
+  @IsInt()
+  classId?: number;
 }
 
 export class UpdateStudentDto {