feat: add TypeORM CLI migration support

- 新增 datasource.ts 支持 mysql/sqlite 双模式
- 新增 migration 脚本: generate/create/run/revert/show
- 生成 InitialSchema migration (35 张表全量建表)

apps/server/datasource.ts

@@ -0,0 +1,21 @@
+import { DataSource } from 'typeorm';
+import { config } from 'dotenv';
+import { join } from 'path';
+
+// TypeORM CLI runs from apps/server/
+const root = process.cwd();
+config({ path: join(root, '.env') });
+
+const dbType = process.env.DB_TYPE || 'sqlite';
+
+export default new DataSource({
+  type: dbType === 'mysql' ? 'mysql' : 'better-sqlite3',
+  host: dbType === 'mysql' ? (process.env.DB_HOST || 'localhost') : undefined,
+  port: dbType === 'mysql' ? (Number(process.env.DB_PORT) || 3306) : undefined,
+  username: dbType === 'mysql' ? (process.env.DB_USERNAME || 'root') : undefined,
+  password: dbType === 'mysql' ? (process.env.DB_PASSWORD || '') : undefined,
+  database: process.env.DB_DATABASE || (dbType === 'mysql' ? 'dorm_billing' : 'dorm_billing.db'),
+  charset: dbType === 'mysql' ? 'utf8mb4' : undefined,
+  entities: [join(root, 'src/**/*.entity.ts')],
+  migrations: [join(root, 'src/migrations/*.ts')],
+});