feat(validation): replace fieldValidation with express-validator on products and tags

Add products.validators.js and tags.validators.js following the same
pattern as articles/users. Wire createProductRules, updateProductRules,
and createTagRules into their respective routes via the validate middleware.
Remove the local fieldValidation helper from both controllers and fix
missing return statements on next() calls in products.controller.js.

src/routes/api/cms/tags.routes.js

@@ -1,10 +1,12 @@
 const express = require('express');
 const { createTag, deleteTag, getAllTags } = require('../../../controllers/tags.controller');
 const auth = require('../../../middlewares/auth');
+const validate = require('../../../middlewares/validate');
+const { createTagRules } = require('../../../middlewares/validators/tags.validators');
 
 const tagRouter = express.Router();
 
-tagRouter.post('/', auth.required, createTag);
+tagRouter.post('/', auth.required, createTagRules, validate, createTag);
 tagRouter.get('/', auth.optional, getAllTags);
 tagRouter.delete('/:name', auth.required, deleteTag);