fix: schedule nightly index rebuild on worker and skip per-ingest rebuild.

Ingest relies on SurrealDB incremental index maintenance; the worker runs native REBUILD INDEX on a configurable interval with lease state on system_settings.

html-router/src/routes/admin/handlers.rs

@@ -350,6 +350,9 @@ mod tests {
             image_processing_model: "gpt-4o-mini".into(),
             image_processing_prompt: "p".into(),
             voice_processing_model: "whisper-1".into(),
+            last_index_rebuild_at: None,
+            index_rebuild_lease_owner: None,
+            index_rebuild_lease_expires_at: None,
         }
     }