feat: 初始版本，圆角主题与首次管理员引导

app/extensions.py

@@ -0,0 +1,9 @@
+from flask_sqlalchemy import SQLAlchemy
+from flask_migrate import Migrate
+from flask_login import LoginManager
+from flask_wtf import CSRFProtect
+
+db = SQLAlchemy()
+migrate = Migrate()
+login_manager = LoginManager()
+csrf = CSRFProtect()