* fix(proxy): check previous_response_id ownership on /v1/responses/compact
* test(proxy): cover the unmanaged response id escape hatches on every response id route
* test(proxy): audit compact previous_response_id ownership
Add integration cells for the native /v1/responses/compact routes covering owner,
admin, cross-tenant, unmanaged, malformed, duplicated and retained ids, provider
errors, the response cache, id-security settings, an upstream outage, a held
upstream, a worker kill and a proxy restart. Unskip the provider wire cell whose
bug this branch fixes.
* test(proxy): cover the no signing key path on every response id route
