Changes to Start a CUA task

the llm request property default value changed from computer-use-preview to gpt-5.6-terra

added the new gpt-6.1-terra enum value to the request property llm

added subschema #4 to the sessionOptions/credentials/items request property oneOf list

added the new optional request property sessionOptions/credentials

added the new optional request property sessionOptions/proxyRoutes

added the new optional request property sessionOptions/webBotAuth

added the new optional request property sessionOptions/enableWebMcp

added the new gpt-6.1-sol enum value to the request property llm

added the new gpt-6-luna enum value to the request property llm

added the new gpt-6-sol enum value to the request property llm

added the new optional request property reasoningEffort

added the new gpt-6-astra enum value to the request property llm

added the new us enum value to the request property sessionOptions/region

added the new gpt-5.5 enum value to the request property llm

added the new gpt-5.6-luna enum value to the request property llm

added the new gpt-5.6-sol enum value to the request property llm

added the new gpt-5.6-terra enum value to the request property llm