feat(payment): 实现网页端登录码流程（无需微信登录）

- 新增 GET /payment/generate-code：网页端生成 ASD-XXXXXX 登录码
- 新增 GET /payment/login-status：网页轮询查询登录码确认状态
- web_generate_login_code 和 web_login_confirm 增加 JWT 保护
- payment_index JS 改为真实调用 generate-code 并轮询
- 添加 rand crate 依赖

src/handlers/mod.rs

@@ -37,8 +37,10 @@ pub use weather::post_weather_data;
 pub use payment::alipay_notify;
 pub use payment::alipay_pay_page;
 pub use payment::create_order;
+pub use payment::generate_code;
 pub use payment::get_user_quota;
 pub use payment::mock_confirm;
 pub use payment::payment_index;
+pub use payment::payment_login_status;
 pub use payment::payment_page;
 pub use payment::payment_success;