fix(auth): replace normalizeEmail with toLowerCase to prevent Gmail dot-stripping

normalizeEmail() transforms e.g. user.name@gmail.com → username@gmail.com
(removes dots per Gmail aliasing rules), causing a mismatch between the
stored email and the value Passport searches for at login. Replaced with
toLowerCase() which is the only normalization applied consistently by
create-user.js and the rest of the app.

src/middlewares/validators/users.validators.js

@@ -4,7 +4,7 @@ const createUserRules = [
     body('user.email')
         .notEmpty().withMessage("can't be blank")
         .isEmail().withMessage('must be a valid email address')
-        .normalizeEmail(),
+        .toLowerCase(),
     body('user.username')
         .notEmpty().withMessage("can't be blank")
         .isLength({ min: 3, max: 50 }).withMessage('must be between 3 and 50 characters')
@@ -18,7 +18,7 @@ const loginRules = [
     body('user.email')
         .notEmpty().withMessage("can't be blank")
         .isEmail().withMessage('must be a valid email address')
-        .normalizeEmail(),
+        .toLowerCase(),
     body('user.password')
         .notEmpty().withMessage("can't be blank"),
 ];
@@ -44,7 +44,7 @@ const updateEmailRules = [
     body('user.email')
         .notEmpty().withMessage("can't be blank")
         .isEmail().withMessage('must be a valid email address')
-        .normalizeEmail(),
+        .toLowerCase(),
 ];
 
 const updateUsernameRules = [