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

Cargo.toml

@@ -16,6 +16,7 @@ include_dir = "0.7.4"
 jsonwebtoken = "9.3.1"
 log = "0.4.28"
 openssl = "0.10.73"
+rand = "0.8"
 reqwest = { version = "0.12.23", features=["json"]}
 serde = { version = "1.0.219", features = ["derive"] }
 serde_json = "1.0.143"