feat(deploy): 一条命令链部署——双单文件 + Caddy + DATABASE_URL 单源

多阶段镜像编出 server/engine 单文件与前端静态；compose 起 pg/server/engine/caddy；
启动时自动迁移；仅用 DATABASE_URL，postgres 建库参数由 entrypoint 拆解。

packages/db/src/index.ts

@@ -1,4 +1,5 @@
 import { drizzle } from "drizzle-orm/postgres-js";
+import { migrate } from "drizzle-orm/postgres-js/migrator";
 import postgres from "postgres";
 import * as schema from "./schema.ts";
 
@@ -9,5 +10,10 @@ export function createDb(connectionString: string) {
 
 export type Db = ReturnType<typeof createDb>;
 
+/** 启动时按 journal 应用缺失迁移（幂等）；`migrationsFolder` 指向 drizzle/ 目录 */
+export async function runMigrations(db: Db, migrationsFolder: string) {
+  await migrate(db, { migrationsFolder });
+}
+
 export * from "./schema.ts";
 export * from "./repos.ts";