feat: add Bedrock API key as a managed auth mode (#27443)

## Why

Codex needs to manage Amazon Bedrock API key credentials through the
existing auth lifecycle instead of introducing a separate auth manager
or provider-specific credential file. Treating Bedrock API key login as
a primary auth mode gives it the same persistence, keyring, reload, and
logout behavior as the existing OpenAI API key and ChatGPT modes.

The credential is valid only for the `amazon-bedrock` model provider.
OpenAI-compatible providers must reject this auth mode rather than
treating the Bedrock key as an OpenAI bearer token.

## What changed

- Added `bedrockApiKey` as an app-server `AuthMode` and
`CodexAuth::BedrockApiKey` as a primary `AuthManager` mode.
- Added `BedrockApiKeyAuth`, containing the API key and AWS region, to
the existing `AuthDotJson` payload stored in `$CODEX_HOME/auth.json` or
the configured keyring backend.
- Added `login_with_bedrock_api_key(...)`, parallel to
`login_with_api_key(...)`, which replaces the current stored login with
Bedrock credentials.
- Reused generic auth reload and logout behavior instead of adding a
Bedrock-specific auth manager or logout path.
- Updated login restrictions, status reporting, diagnostics, telemetry
classification, generated app-server schemas, and auth fixtures for the
new mode.
- Added explicit errors when Bedrock API key auth is selected with an
OpenAI-compatible model provider.

This PR establishes managed storage and auth-mode behavior. Routing the
managed key and region into Amazon Bedrock requests will be in follow-up
PRs.

codex-rs/app-server/tests/common/auth_fixtures.rs

@@ -165,6 +165,7 @@ pub fn write_chatgpt_auth(
         last_refresh,
         agent_identity: None,
         personal_access_token: None,
+        bedrock_api_key: None,
     };
 
     save_auth(codex_home, &auth, cli_auth_credentials_store_mode).context("write auth.json")

codex-rs/app-server/tests/suite/v2/app_list.rs

@@ -119,6 +119,7 @@ async fn list_apps_returns_empty_with_api_key_auth() -> Result<()> {
             last_refresh: None,
             agent_identity: None,
             personal_access_token: None,
+            bedrock_api_key: None,
         },
         AuthCredentialsStoreMode::File,
     )?;