refactor(categories): change controller route from 'api/categories' to 'categories'

fix(products): update category fetch logic to ensure data is an array
refactor(products): simplify GET handler by integrating authentication directly

backend/src/categories/categories.controller.ts

@@ -2,7 +2,7 @@ import { Controller, Get } from '@nestjs/common';
 import { CategoriesService } from './categories.service';
 import { Public } from '../auth/decorators/public.decorator';
 
-@Controller('api/categories')
+@Controller('categories')
 export class CategoriesController {
   constructor(private readonly categoriesService: CategoriesService) {}