Native /login and /logout (plus setup-wizard sign-in and RPC login)
refreshed model discovery with the default all-provider
online-if-uncached strategy, which reused a fresh authoritative cache row
and never re-ran fetchDynamicModels with the just-persisted credential,
so newly authenticated models stayed unavailable in-session and stale
endpoint data survived a relogin. Each auth-completion path now awaits a
provider-scoped refreshProvider(providerId, "online").
Also fixed writeModelCache serializing credential-bearing request headers
(Authorization, X-Api-Key, api-key, cookie, proxy-authorization) into the
plaintext models.db; they are now stripped before persistence and
re-derived on load from AuthStorage / provider config.
Fixes#5780
