refactor(backend): replace unwraps with typed errors

backend/src/web/mw_auth.rs

@@ -29,6 +29,7 @@ pub async fn mw_ctx_resolver(
         Some(token) => user_repository
             .get_session(&token)
             .await
+            .and_then(|s| s.ok_or(LoftError::AuthFailSessionNotFound))
             .map(|s| Ctx::new(s.user_id)),
         None => Err(LoftError::AuthFailNoAuthTokenCookie),
     };