[codex] Propagate rate limit reached type (#18227)

## Summary

First PR in the split from #17956.

- adds the core/app-server `RateLimitReachedType` shape
- maps backend `rate_limit_reached_type` into Codex rate-limit snapshots
- carries the field through app-server notifications/responses and
generated schemas
- updates existing constructors/tests for the new optional field

## Validation

- `cargo test -p codex-backend-client`
- `cargo test -p codex-app-server-protocol`
- `cargo test -p codex-app-server rate_limits`
- `cargo test -p codex-tui workspace_`
- `cargo test -p codex-tui status_`
- `just fmt`
- `just fix -p codex-backend-client`
- `just fix -p codex-app-server-protocol`
- `just fix -p codex-app-server`
- `just fix -p codex-tui`

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

@@ -7,6 +7,7 @@ use codex_app_server_protocol::GetAccountRateLimitsResponse;
 use codex_app_server_protocol::JSONRPCError;
 use codex_app_server_protocol::JSONRPCResponse;
 use codex_app_server_protocol::LoginAccountResponse;
+use codex_app_server_protocol::RateLimitReachedType;
 use codex_app_server_protocol::RateLimitSnapshot;
 use codex_app_server_protocol::RateLimitWindow;
 use codex_app_server_protocol::RequestId;
@@ -118,6 +119,9 @@ async fn get_account_rate_limits_returns_snapshot() -> Result<()> {
                 "reset_at": secondary_reset_timestamp,
             }
         },
+        "rate_limit_reached_type": {
+            "type": "workspace_member_usage_limit_reached",
+        },
         "additional_rate_limits": [
             {
                 "limit_name": "codex_other",
@@ -173,6 +177,7 @@ async fn get_account_rate_limits_returns_snapshot() -> Result<()> {
             }),
             credits: None,
             plan_type: Some(AccountPlanType::Pro),
+            rate_limit_reached_type: Some(RateLimitReachedType::WorkspaceMemberUsageLimitReached),
         },
         rate_limits_by_limit_id: Some(
             [
@@ -193,6 +198,9 @@ async fn get_account_rate_limits_returns_snapshot() -> Result<()> {
                         }),
                         credits: None,
                         plan_type: Some(AccountPlanType::Pro),
+                        rate_limit_reached_type: Some(
+                            RateLimitReachedType::WorkspaceMemberUsageLimitReached,
+                        ),
                     },
                 ),
                 (
@@ -208,6 +216,7 @@ async fn get_account_rate_limits_returns_snapshot() -> Result<()> {
                         secondary: None,
                         credits: None,
                         plan_type: Some(AccountPlanType::Pro),
+                        rate_limit_reached_type: None,
                     },
                 ),
             ]