[Bug] RelatedPostsFactory throws runtime error / fails when blog posts have empty or null tags

🐛 Bug Description

When a blog post's frontmatter has an empty tags: field (or tags: null), RelatedPostsFactory fails with runtime errors and prevents the "Related Posts" section from properly calculating recommendations.

There are two failure modes:

1. Current post has no tags: RelatedPostsFactory.getPosts() logs "RelatedPostsFactory: Tags not provided, use setTags()." and returns an empty array [], completely skipping category-based recommendations.
2. Candidate post in the pool has no tags: addTagsPoints() in src/components/Related-Posts/relatedPostsFactory.js:69 invokes .forEach() directly on post.frontmatter.tags with no null check, throwing TypeError: Cannot read properties of null (reading 'forEach').

📍 Location of Bug

• File: src/components/Related-Posts/relatedPostsFactory.js
• Lines: 34–37 and 65–74

const addTagsPoints = (post, tags) => {
  const tagPoint = 1;
  const slug = getSlug(post);

  // 💥 Crashes when post.frontmatter.tags is null
  post.frontmatter.tags.forEach((tag) => {
    if (includes(tags, tag)) {
      identityMap[slug].points += tagPoint;
    }
  });
};