feat(engine): 实现同步引擎与 engine_status 快照

apps/engine 独立进程（syncRound + 防重叠调度）；上游 log/token；QPU 采样；
server 读 engine_status；时刻出参 toUnixSec；中文日志；zod-openapi 扩展顺序修复。

apps/engine/src/index.ts

@@ -0,0 +1,29 @@
+import { appLogger, setupLogging } from "@new-api-key-usage/core";
+import { createDb, createRepos } from "@new-api-key-usage/db";
+import { loadEnv } from "./env.ts";
+import { createSyncLoop } from "./loop.ts";
+
+const env = loadEnv(process.env);
+setupLogging(env.LOG_LEVEL);
+const log = appLogger("engine");
+
+const db = createDb(env.DATABASE_URL);
+const repos = createRepos(db);
+
+const loop = createSyncLoop({
+  repos,
+  newapiBase: env.NEWAPI_BASE,
+  skKeyEncryptionSecret: env.SK_KEY_ENCRYPTION_SECRET,
+  intervalMs: env.SYNC_INTERVAL_MS,
+});
+
+loop.start();
+
+log.info`apps/engine 已就绪`;
+
+process.on("SIGINT", () => {
+  void loop.stop().then(() => process.exit(0));
+});
+process.on("SIGTERM", () => {
+  void loop.stop().then(() => process.exit(0));
+});