feat: add student wallet utility billing

apps/server/src/entities/personal-expense.entity.ts

@@ -34,6 +34,9 @@ export class PersonalExpense {
   @Column({ name: 'recorded_by', nullable: true })
   recordedBy: number;
 
+  @Column({ name: 'bill_id', type: 'integer', nullable: true })
+  billId: number | null;
+
   @CreateDateColumn({ name: 'created_at' })
   createdAt: Date;