feat: Iteration 1 — 审计日志IP记录、文件上传、医护端API、小程序角色切换

Iteration 1 六项任务全部完成：

1. 审计日志IP记录 — task_local RequestInfo 自动注入 IP/user_agent
2. 文件上传服务 — multipart 上传 + ServeDir 静态文件服务
3. 医护端后端API — 医生工作台仪表盘 + 患者标签CRUD + 会话已读
4. 小程序角色切换 — 登录后根据角色跳转医护台/患者首页
5. 小程序安全加固 — secure-storage 开发模式警告
6. 讨论记录归档 — docs/discussions/

Cargo.toml

@@ -31,7 +31,7 @@ tokio = { version = "1", features = ["full"] }
 # Web
 axum = { version = "0.8", features = ["multipart"] }
 tower = "0.5"
-tower-http = { version = "0.6", features = ["cors", "trace", "compression-gzip"] }
+tower-http = { version = "0.6", features = ["cors", "trace", "compression-gzip", "fs"] }
 
 # Database
 sea-orm = { version = "1.1", features = [