feat: expose AWS account state from account/read (#19048)

## Why

AWS/Bedrock mode currently reports `account: null` with
`requiresOpenaiAuth: false` from `account/read`. That suppresses the
OpenAI-auth requirement, but it does not let app clients distinguish AWS
auth from any other non-OpenAI custom provider. For the prototype AWS
provider UX, clients need a simple provider-derived signal so they can
suppress ChatGPT/API-key login and token-refresh paths without
hardcoding Bedrock checks.

## What changed

- Adds an `aws` variant to the v2 `Account` protocol union.
- Adds `ProviderAccountKind` to `codex-model-provider` so the runtime
provider owns the app-visible account classification.
- Makes Amazon Bedrock return `ProviderAccountKind::Aws` from the
model-provider layer.
- Updates app-server `account/read` to map `ProviderAccountKind` to the
existing `GetAccountResponse` wire shape.
- Preserves the existing `account: null, requiresOpenaiAuth: false`
behavior for other non-OpenAI providers.
- Regenerates the app-server protocol schema fixtures.
- Adds coverage for provider account classification and for the Amazon
Bedrock `account/read` response.

## Testing

- `cargo test -p codex-model-provider`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server get_account_with_aws_provider`

## Notes

I attempted `just bazel-lock-update` and `just bazel-lock-check`, but
both are blocked in my local environment because `bazel` is not
installed.

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -7,6 +7,7 @@ use crate::RequestId;
 use crate::protocol::common::AuthMode;
 use codex_experimental_api_macros::ExperimentalApi;
 use codex_protocol::account::PlanType;
+use codex_protocol::account::ProviderAccount;
 use codex_protocol::approvals::ElicitationRequest as CoreElicitationRequest;
 use codex_protocol::approvals::ExecPolicyAmendment as CoreExecPolicyAmendment;
 use codex_protocol::approvals::GuardianAssessmentAction as CoreGuardianAssessmentAction;
@@ -2015,6 +2016,20 @@ pub enum Account {
     #[serde(rename = "chatgpt", rename_all = "camelCase")]
     #[ts(rename = "chatgpt", rename_all = "camelCase")]
     Chatgpt { email: String, plan_type: PlanType },
+
+    #[serde(rename = "amazonBedrock", rename_all = "camelCase")]
+    #[ts(rename = "amazonBedrock", rename_all = "camelCase")]
+    AmazonBedrock {},
+}
+
+impl From<ProviderAccount> for Account {
+    fn from(account: ProviderAccount) -> Self {
+        match account {
+            ProviderAccount::ApiKey => Self::ApiKey {},
+            ProviderAccount::Chatgpt { email, plan_type } => Self::Chatgpt { email, plan_type },
+            ProviderAccount::AmazonBedrock => Self::AmazonBedrock {},
+        }
+    }
 }
 
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, JsonSchema, TS, ExperimentalApi)]