feat(task1): restructure directories for turborepo monorepo

- Move backend/ to apps/server/ via git mv
- Move frontend/ to apps/admin/ via git mv
- Create packages/typescript-config/ with base, nestjs, and react-vite presets

apps/server/src/entities/bill-item.entity.ts

@@ -0,0 +1,36 @@
+import { Entity, PrimaryGeneratedColumn, Column, ManyToOne, JoinColumn } from 'typeorm';
+import { Bill } from './bill.entity';
+
+@Entity('bill_items')
+export class BillItem {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  @Column({ name: 'bill_id' })
+  billId: number;
+
+  @Column({ name: 'room_id', nullable: true })
+  roomId: number;
+
+  @Column({ name: 'expense_type', length: 20, nullable: true })
+  expenseType: string;
+
+  @Column({ length: 200, nullable: true })
+  description: string;
+
+  @Column({ nullable: true })
+  days: number;
+
+  @Column({ name: 'total_room_days', nullable: true })
+  totalRoomDays: number;
+
+  @Column({ name: 'room_total_amount', type: 'decimal', precision: 10, scale: 2, nullable: true })
+  roomTotalAmount: number;
+
+  @Column({ name: 'student_amount', type: 'decimal', precision: 10, scale: 2, nullable: true })
+  studentAmount: number;
+
+  @ManyToOne(() => Bill, (b) => b.items)
+  @JoinColumn({ name: 'bill_id' })
+  bill: Bill;
+}