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/tests/utils/mock_email.rs

@@ -0,0 +1,23 @@
+use std::sync::Arc;
+
+use recipes::email;
+
+pub struct MockEmailService;
+
+impl MockEmailService {
+    pub fn create_service() -> Arc<dyn email::EmailServiceTrait> {
+        Arc::new(Self {})
+    }
+}
+
+#[async_trait::async_trait]
+impl email::EmailServiceTrait for MockEmailService {
+    async fn send_email(
+        &self,
+        _email: &str,
+        _title: &str,
+        _message: &str,
+    ) -> Result<(), email::Error> {
+        Ok(())
+    }
+}