Function classify_node_type 

pub fn classify_node_type(node_type: &str) -> NodeKind

Classify a node’s op-key / component token into NodeKind.

The MCP convention keys on the exact token mcp. Because server and tool now live in the payload (not the key), this classifier returns an NodeKind::Mcp with empty server_id/tool; callers populate those from the payload via mcp_server_and_tool during load/validate.

MCP takes precedence over the adapter convention. Everything else falls back to the adapter split or NodeKind::Builtin.