fix(operation-trace): satisfy ruff/codeql and drop a dead summary channel

- Remove the unused request_summary local: the stored summary is derived by the
  service from changes + the classified action, so handlers publishing
  quart.g.operation_log_summary was a dead channel that never reached the row.
- Drop the unused datetime import in the operation log model.
- Apply ruff format to the touched files so `ruff format --check` passes.

src/langbot/pkg/api/http/controller/group.py

@@ -413,12 +413,13 @@ class RouterGroup(abc.ABC):
             # static route declaration cannot describe the runtime diff, e.g.
             # the previous and the new role of a member. ``quart.g`` is
             # request-local, so concurrent requests never share these values.
+            # The stored summary is derived by the service from ``changes`` and
+            # the classified action, so handlers only publish the diff itself.
             changes = resolved_meta.get('changes')
             detail = resolved_meta.get('detail')
             request_changes = getattr(quart.g, 'operation_log_changes', None)
             request_detail = getattr(quart.g, 'operation_log_detail', None)
             request_resource_id = getattr(quart.g, 'operation_log_resource_id', None)
-            request_summary = getattr(quart.g, 'operation_log_summary', None)
             if request_changes:
                 changes = request_changes
             if request_detail: