fix(config): add openai-codex-responses to ModelApiSchema

The config schema validates provider api fields against ModelApiSchema,
but openai-codex-responses was missing from the allowed values. This
forces users to set api: "openai-responses" for the openai-codex
provider, which routes requests to api.openai.com/v1/responses instead
of chatgpt.com/backend-api/codex/responses, causing HTTP 401 errors
because Codex OAuth tokens lack api.responses.write scope for the
standard OpenAI Responses endpoint.

The runtime already supports openai-codex-responses throughout: model
registry, stream dispatch (streamOpenAICodexResponses), and provider
detection (OPENAI_MODEL_APIS set). Only the config schema was missing
the literal.

src/config/zod-schema.core.ts

@@ -182,6 +182,7 @@ export const SecretsConfigSchema = z
 export const ModelApiSchema = z.union([
   z.literal("openai-completions"),
   z.literal("openai-responses"),
+  z.literal("openai-codex-responses"),
   z.literal("anthropic-messages"),
   z.literal("google-generative-ai"),
   z.literal("github-copilot"),