fix: limit global search to 9 IDs and fix more_like_this_ids off-by-one

Global search only displays 3 results but was fetching all matching IDs
and hydrating them via in_bulk. Now passes limit=9 to search_ids().

more_like_this_ids could return limit-1 results when the original doc
appeared in the result set. Now fetches limit+1 and slices after
filtering.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/documents/search/_backend.py

@@ -762,14 +762,16 @@ class TantivyBackend:
         final_query = self._apply_permission_filter(mlt_query, user)
 
         effective_limit = limit if limit is not None else searcher.num_docs
-        results = searcher.search(final_query, limit=effective_limit)
+        # Fetch one extra to account for excluding the original document
+        results = searcher.search(final_query, limit=effective_limit + 1)
 
         ids = []
         for _score, doc_address in results.hits:
             result_doc_id = searcher.doc(doc_address).to_dict()["id"][0]
             if result_doc_id != doc_id:
                 ids.append(result_doc_id)
-        return ids
+
+        return ids[:limit] if limit is not None else ids
 
     def batch_update(self, lock_timeout: float = 30.0) -> WriteBatch:
         """

src/documents/views.py

@@ -3136,6 +3136,7 @@ class GlobalSearchView(PassUserMixin):
                     query,
                     user=user,
                     search_mode=SearchMode.TEXT,
+                    limit=OBJECT_LIMIT * 3,
                 )
                 docs_by_id = all_docs.in_bulk(matching_ids)
                 docs = [