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>

internal/agent/agent.go

@@ -35,11 +35,12 @@ type Agent struct {
 	Proxy     *ProxyRouter
 	Certs     *CertProvisioner
 	DNS       *DNSRegistrar
+	Version   string
 }
 
 // Run starts the agent: opens the database, sets up the gRPC server with
 // TLS and auth, and blocks until SIGINT/SIGTERM.
-func Run(cfg *config.AgentConfig) error {
+func Run(cfg *config.AgentConfig, version string) error {
 	logger := slog.New(slog.NewTextHandler(os.Stderr, &slog.HandlerOptions{
 		Level: parseLogLevel(cfg.Log.Level),
 	}))
@@ -79,6 +80,7 @@ func Run(cfg *config.AgentConfig) error {
 		Proxy:     proxy,
 		Certs:     certs,
 		DNS:       dns,
+		Version:   version,
 	}
 
 	tlsCert, err := tls.LoadX509KeyPair(cfg.Server.TLSCert, cfg.Server.TLSKey)