auth: move domain mode below app wire types (#29721)

## Why

Authentication mode is a domain concept used by login, model selection,
telemetry, and transports. Keeping the canonical type in app-server
protocol forces those lower-level crates to depend on an unrelated wire
API.

## What changed

- Added canonical `codex_protocol::auth::AuthMode` domain values.
- Kept the app-server wire DTO unchanged and added an explicit app-side
conversion.
- Removed production app-server-protocol dependencies from login,
model-provider-info, models-manager, and otel call paths.

## Stack

This is PR 2 of 6, stacked on [PR
#29714](https://github.com/openai/codex/pull/29714). Review only the
delta from `codex/split-json-rpc-protocols`. Next: [PR
#29722](https://github.com/openai/codex/pull/29722).

## Validation

- Auth and login coverage passed in the focused protocol/domain test
run.
- App-server account and auth conversion coverage passed.

codex-rs/core/src/client_tests.rs

@@ -16,7 +16,6 @@ use crate::test_support::responses_metadata as test_responses_metadata;
 use codex_api::ApiError;
 use codex_api::ResponseEvent;
 use codex_api::TransportError;
-use codex_app_server_protocol::AuthMode;
 use codex_login::AuthManager;
 use codex_login::CodexAuth;
 use codex_model_provider::BearerAuthProvider;
@@ -28,6 +27,7 @@ use codex_model_provider_info::WireApi;
 use codex_model_provider_info::create_oss_provider_with_base_url;
 use codex_otel::SessionTelemetry;
 use codex_protocol::ThreadId;
+use codex_protocol::auth::AuthMode;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::openai_models::ModelInfo;