零 Node 部署、超级管理员，并完善本地构建发布文档。

- FastAPI 单进程托管 frontend/dist，systemd 替代 PM2

- 超级管理员 admin、注册开关与用户管理

- README/DEPLOY/USAGE 说明：改代码须本地构建 dist 后 push，服务器 update.sh

- 提交 frontend/dist 与 build-frontend 脚本

backend/app/services/migrate.py

@@ -1,5 +1,6 @@
 from sqlalchemy import inspect, text
 
+from app.core.config import settings
 from app.core.database import engine
 
 
@@ -18,3 +19,17 @@ def run_migrations() -> None:
                     "NOT NULL DEFAULT 'junior_high'"
                 )
             )
+
+    if "users" in inspector.get_table_names():
+        user_columns = {col["name"] for col in inspector.get_columns("users")}
+        if "is_superuser" not in user_columns:
+            with engine.begin() as conn:
+                conn.execute(
+                    text("ALTER TABLE users ADD COLUMN is_superuser BOOLEAN NOT NULL DEFAULT FALSE")
+                )
+                conn.execute(
+                    text(
+                        f"UPDATE users SET is_superuser = TRUE "
+                        f"WHERE username = '{settings.ADMIN_DEFAULT_USERNAME}'"
+                    )
+                )