1. Add 登陆功能

2. 调整字体大小
3. 新增部分功能

backend/app/infrastructure/auth/__init__.py

@@ -0,0 +1,5 @@
+"""JWT token creation and validation infrastructure.
+
+JWTHandler is the only component in this package. It is wired through
+shared/bootstrap.py and injected into FastAPI dependencies.
+"""