fix(proxy): shape direct OpenAI reasoning chat payloads

src/proxy/transformers/request-transformer.ts

@@ -127,6 +127,7 @@ export interface ProxyOpenAIRequest {
   parallel_tool_calls?: boolean;
   messages: OpenAIMessage[];
   max_tokens?: number;
+  max_completion_tokens?: number;
   temperature?: number;
   top_p?: number;
   stop?: string[];