Blog category filter is lost when loading more posts

## Description When browsing the blog with a category filter selected, the first page is filtered correctly, but loading the next page loses the category parameter. As a result, posts from other categories can be appended to the filtered list. ## Steps to reproduce 1. Open the blog page. 2. Select a category such as `postgres`. 3. Make sure the category has more than 25 posts. 4. Scroll to the bottom to trigger loading more posts. 5. Inspect the second request to `/api-v2/blog-posts`. ## Expected behavior Every paginated request preserves the selected category: `/api-v2/blog-posts?offset=25&limit=25&category=postgres` ## Actual behavior The second request omits the category: `/api-v2/blog-posts?offset=25&limit=25` Posts from other categories are then appended to the current filtered list. ## Root cause `handleFilterChange()` stores the selected category in `filterParams`, but `fetchMorePosts()` only adds `filterParams.search` to subsequent requests. This behavior was introduced by the blog layout changes in #47236, which removed the existing category parameter from `fetchMorePosts()`. ## Proposed fix Add the stored category to subsequent requests when it is not `all`.