Update dependencies and implement email service integration

- Refactor app and email modules to include email service
- Add tests for user sign-up and mock email service

backend/src/lib.rs

@@ -2,9 +2,9 @@ pub mod app;
 pub mod config;
 pub mod consts;
 pub mod data;
+pub mod email;
 pub mod log;
 
-mod email;
 mod hash;
 mod html_templates;
 mod ron_extractor;