Adds push_retries_after_401_on_expired_access_token to sync_round_trip.rs,
closing the push-side coverage gap alongside the existing pull test
(jwt_refresh_on_401_succeeds). Both tests use an expired-but-validly-signed
access token to trigger the 401 → refresh → retry path in
SolitaireServerClient.
Also exposes build_test_pool() from solitaire_server so downstream crates
can boot a test server without duplicating the migration boilerplate.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
funman300
198df75f94