feat(codex): support ultrafast service tier

Accept service_tier=ultrafast on the OpenAI/Codex gateway, advertise it
on GPT-5.6 Sol in the Codex model catalog, and include it in ChatGPT
OAuth routing hints so Codex clients can select Ultrafast.

frontend/src/api/admin/settings.ts

@@ -1429,7 +1429,7 @@ export async function updateRectifierSettings(
  * Matches backend dto.OpenAIFastPolicyRule.
  */
 export interface OpenAIFastPolicyRule {
-  service_tier: "all" | "priority" | "flex";
+  service_tier: "all" | "priority" | "flex" | "ultrafast";
   action: "pass" | "filter" | "block" | "force_priority";
   scope: "all" | "oauth" | "apikey" | "bedrock";
   user_ids?: number[];