fix: address code review findings (int keys, docstring, empty ordering)

- TantivyRelevanceList.__getitem__ now handles int keys, not just slices
- search_ids() docstring corrected ("no highlights or scores")
- Empty ordering param now correctly becomes None instead of ""

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

src/documents/search/_backend.py

@@ -133,7 +133,17 @@ class TantivyRelevanceList:
     def __len__(self) -> int:
         return len(self._ordered_ids)
 
-    def __getitem__(self, key: slice) -> list[SearchHit]:
+    def __getitem__(self, key: int | slice) -> SearchHit | list[SearchHit]:
+        if isinstance(key, int):
+            idx = key if key >= 0 else len(self._ordered_ids) + key
+            if self._page_offset <= idx < self._page_offset + len(self._page_hits):
+                return self._page_hits[idx - self._page_offset]
+            return SearchHit(
+                id=self._ordered_ids[key],
+                score=0.0,
+                rank=idx + 1,
+                highlights={},
+            )
         start = key.start or 0
         stop = key.stop or len(self._ordered_ids)
         # DRF slices to extract the current page.  If the slice aligns
@@ -748,7 +758,7 @@ class TantivyBackend:
         limit: int | None = None,
     ) -> list[int]:
         """
-        Return document IDs matching a query — no highlights, no stored doc fetches.
+        Return document IDs matching a query — no highlights or scores.
 
         This is the lightweight companion to search(). Use it when you need the
         full set of matching IDs (e.g. for ``selection_data``) but don't need

src/documents/views.py

@@ -2083,7 +2083,7 @@ class UnifiedSearchViewSet(DocumentViewSet):
             # Parse ordering param
             ordering_param = request.query_params.get("ordering", "")
             sort_reverse = ordering_param.startswith("-")
-            sort_field_name = ordering_param.lstrip("-") if ordering_param else None
+            sort_field_name = ordering_param.lstrip("-") or None
 
             use_tantivy_sort = (
                 sort_field_name in TantivyBackend.SORTABLE_FIELDS