Terminal relay: answer Hammerhead's terminal sessions through the agent

When someone opens a terminal for this site, Hammerhead lists the session in the
site's config. The agent connects out to Hammerhead and joins that connection to
its own SSH server, so no port has to be open on an edge. The agent now reports
where its SSH server listens and that it can relay.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

cmd/bamboo/main.go

@@ -79,6 +79,7 @@ func main() {
 	if dc.Ports, err = discover.ParsePorts(*discoverPorts); err != nil {
 		log.Fatalf("-discover-ports: %v", err)
 	}
+	sshAddr := "" // reported to Hammerhead, so its terminal can reach the server through this agent
 	if *sshOn {
 		if !sshd.Supported {
 			log.Fatal("-ssh: the SSH server is not available on this platform")
@@ -91,6 +92,7 @@ func main() {
 		if err != nil {
 			log.Fatalf("-ssh: %v", err)
 		}
+		sshAddr = *sshListen
 		log.Printf("ssh: listening on %s, host key %s", *sshListen, srv.Fingerprint())
 		go func() {
 			if err := srv.Run(ctx); err != nil {
@@ -98,7 +100,7 @@ func main() {
 			}
 		}()
 	}
-	b, err := bamboo.New(bamboo.Config{Hammerhead: strings.TrimRight(*hh, "/"), Token: *token, DataDir: *data, Docker: *dockerOn, Discover: dc,
+	b, err := bamboo.New(bamboo.Config{Hammerhead: strings.TrimRight(*hh, "/"), Token: *token, DataDir: *data, Docker: *dockerOn, Discover: dc, SSH: sshAddr,
 		Version: version, AutoUpdate: *autoUpdate,
 		UpdateNow: func(ctx context.Context, progress func(string, int, string)) (string, error) {
 			c := upd