Allow passing an MCP prompt (and its arguments) in SDKs

I believe it's currently impossible to run claude -p "/<my-mcp-server>:<my-prompt>". If I try, Claude reports it's unable to access MCP prompts in non-interactive mode.

I don't see a good reason why this shouldn't be supported: the prompt is still selected by the user, but the users wants to run Claude in fire-and-forget automated fashion.