feat(documents): run the vault's months side by side by default

An account that never picked an arrangement now sees the months flowing
across the width. The layout PUT stores only the fields the person chose,
so an untouched field keeps following the default while a saved choice
stays.

docs/api/openapi.yaml

@@ -71374,7 +71374,7 @@ components:
             - stacked
             - flow
           description: '`stacked` gives every month its own block; `flow` runs the documents across the full width and wraps, with
-            month names inline. Default "stacked".'
+            month names inline. Default "flow"; an account that never chose keeps following the default.'
       required:
         - version
         - view