Add agent version to mcp node list

Thread the linker-injected version string into the Agent struct and
return it in the NodeStatus RPC. The CLI now dials each node and
displays the agent version alongside name and address.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/mcp-agent/main.go

@@ -38,7 +38,7 @@ func main() {
 			if err != nil {
 				return fmt.Errorf("load config: %w", err)
 			}
-			return agent.Run(cfg)
+			return agent.Run(cfg, version)
 		},
 	})