feat: add student wallet utility billing

apps/server/src/entities/student-wallet.entity.ts

@@ -0,0 +1,32 @@
+import {
+  Column,
+  CreateDateColumn,
+  Entity,
+  JoinColumn,
+  OneToOne,
+  PrimaryGeneratedColumn,
+  UpdateDateColumn,
+} from 'typeorm';
+import { Student } from './student.entity';
+
+@Entity('student_wallets')
+export class StudentWallet {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  @Column({ name: 'student_id', type: 'integer', unique: true })
+  studentId: number;
+
+  @Column({ type: 'decimal', precision: 12, scale: 2, default: 0 })
+  balance: number;
+
+  @CreateDateColumn({ name: 'created_at' })
+  createdAt: Date;
+
+  @UpdateDateColumn({ name: 'updated_at' })
+  updatedAt: Date;
+
+  @OneToOne(() => Student, { onDelete: 'CASCADE' })
+  @JoinColumn({ name: 'student_id' })
+  student: Student;
+}