test(core): drop empty metadata dict from after_date regression

SearchIndexRow.to_insert only JSON-serializes truthy metadata
(`if serialize_json and self.metadata`), so passing `metadata={}`
sent a raw dict into the SQLite parameter binding and tripped a
ProgrammingError before the assertions ever ran. Letting metadata
default to None lets the test exercise the after_date / ORDER BY
fix it was written for.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Signed-off-by: Drew Cain <groksrc@gmail.com>

Author: groksrc

tests/services/test_search_service.py

@@ -208,6 +208,9 @@ async def test_after_date_uses_updated_at(search_service):
 
     project_id = search_service.repository.project_id
 
+    # Leave metadata at its None default — SearchIndexRow.to_insert only
+    # JSON-serializes truthy metadata, so passing {} would slip an
+    # un-serialized dict into the SQLite bind and raise ProgrammingError.
     recently_updated_row = SearchIndexRow(
         project_id=project_id,
         id=99001,
@@ -218,7 +221,6 @@ async def test_after_date_uses_updated_at(search_service):
         permalink="test/recently-updated-entity",
         created_at=old_created,
         updated_at=recently_updated,
-        metadata={},
     )
     stale_row = SearchIndexRow(
         project_id=project_id,
@@ -230,7 +232,6 @@ async def test_after_date_uses_updated_at(search_service):
         permalink="test/stale-entity",
         created_at=old_created,
         updated_at=stale_updated,
-        metadata={},
     )
 
     await search_service.repository.index_item(recently_updated_row)