Dedupe blog search results so a post appears only once (#8081)

Mixedbread returns chunk-level matches, and the search route mapped every
chunk to its own page result. A post matching a query in several chunks
(e.g. "Neon" for the Neon pricing post) showed up 2-4 times in the search
dialog. Keep only the first (highest-scoring) chunk per file_id; this also
frees up topK slots for more distinct posts.

Author: nurul3101

apps/blog/src/app/api/search/route.ts

@@ -27,7 +27,12 @@ export const { GET } = createMixedbreadSearchAPI({
   storeIdentifier: "blog-search",
   topK: 20,
   transform: (results, _query) => {
+    // Mixedbread returns chunk-level matches; keep only the highest-scoring
+    // chunk per file so a post never appears more than once.
+    const seenFiles = new Set<string>();
     return results.flatMap((item) => {
+      if (seenFiles.has(item.file_id)) return [];
+      seenFiles.add(item.file_id);
       const metadata = item.generated_metadata as unknown as GeneratedMetadata;
       const slug = (metadata?.slug ?? "").replace(/^\/+/, "");
       const title = metadata?.metaTitle ?? metadata?.title ?? "Untitled";