Move CodexAuth and AuthManager to the core crate (#3074)

Fix a long standing layering issue.

codex-rs/core/tests/suite/compact.rs

@@ -1,5 +1,6 @@
 #![expect(clippy::unwrap_used)]
 
+use codex_core::CodexAuth;
 use codex_core::ConversationManager;
 use codex_core::ModelProviderInfo;
 use codex_core::built_in_model_providers;
@@ -7,7 +8,6 @@ use codex_core::protocol::EventMsg;
 use codex_core::protocol::InputItem;
 use codex_core::protocol::Op;
 use codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR;
-use codex_login::CodexAuth;
 use core_test_support::load_default_config_for_test;
 use core_test_support::wait_for_event;
 use serde_json::Value;