fix(onboarding): tidy the small edges around the setup routes

Four of them. The confirm re-stamped its completion instant on every call, so
a replay quietly moved the moment the setup finished at while the derivation
beside it was carefully latched. The two list answers were stored exactly as
sent, duplicates included, so the column could hold something the reader would
never return — the reader de-duplicates on the way out and now so does the
write. The wide-event name for saving an answer used a different noun from its
two siblings, which makes a dashboard filter awkward for one feature. And the
contract said the restart body was required while the route accepts none.

docs/api/openapi.yaml

@@ -16244,7 +16244,7 @@ paths:
         Cookie or wildcard Bearer, own record only — same refusal under a switch as the answers route. Rate-limited to
         10 restarts per 10 minutes per account.
       requestBody:
-        required: true
+        required: false
         content:
           application/json:
             schema: