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/tenant.entity.ts

@@ -0,0 +1,32 @@
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn, UpdateDateColumn } from 'typeorm';
+
+@Entity('tenants')
+export class Tenant {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  @Column({ length: 100 })
+  name: string;
+
+  @Column({ length: 50, nullable: true })
+  contact: string;
+
+  @Column({ length: 30, nullable: true })
+  phone: string;
+
+  // 可视化颜色（hex），为空时由后端自动分配
+  @Column({ length: 20, nullable: true })
+  color: string;
+
+  @Column({ type: 'text', nullable: true })
+  notes: string;
+
+  @Column({ type: 'varchar', length: 20, default: 'active' })
+  status: string; // active / archived
+
+  @CreateDateColumn({ name: 'created_at' })
+  createdAt: Date;
+
+  @UpdateDateColumn({ name: 'updated_at' })
+  updatedAt: Date;
+}