Tool permission requests fail closed

Control Protocol Query answers a can_use_tool request with an error when no callback is registered, an unknown hook callback ID with an error, and any unsupported request subtype with an error, rather than a default allow. A callback that returns anything other than PermissionResultAllow or PermissionResultDeny is also turned into an error response.

_configure_can_use_tool also routes permission prompts to stdio and refuses to combine can_use_tool with permission_prompt_tool_name, so one gate decides each tool call.