fix: replace broken prev/next links with correct paths (#533)

Nested blog post URLs in the prev/next links were not
updated properly, which resulted in 404 error pages.
This commit updates the outdated URLs to the correct paths.

src/layouts/PostDetails.astro

@@ -69,12 +69,13 @@ const layoutProps = {
 
 /* ========== Prev/Next Posts ========== */
 
-const allPosts = posts.map(({ data: { title }, id }) => ({
-  slug: id,
+const allPosts = posts.map(({ data: { title }, id, filePath }) => ({
+  id,
   title,
+  filePath,
 }));
 
-const currentPostIndex = allPosts.findIndex(a => a.slug === post.id);
+const currentPostIndex = allPosts.findIndex(a => a.id === post.id);
 
 const prevPost = currentPostIndex !== 0 ? allPosts[currentPostIndex - 1] : null;
 const nextPost =
@@ -125,7 +126,7 @@ const nextPost =
       {
         prevPost && (
           <a
-            href={`/posts/${prevPost.slug}`}
+            href={getPath(prevPost.id, prevPost.filePath)}
             class="flex w-full gap-1 hover:opacity-75"
           >
             <IconChevronLeft class="inline-block flex-none" />
@@ -139,7 +140,7 @@ const nextPost =
       {
         nextPost && (
           <a
-            href={`/posts/${nextPost.slug}`}
+            href={getPath(nextPost.id, nextPost.filePath)}
             class="flex w-full justify-end gap-1 text-right hover:opacity-75 sm:col-start-2"
           >
             <div>