feat(boot-test): test.yaml unboundPorts for ports opened only when a player connects

The first real run of the port check found that the crossplay Minecraft
server opens no UDP socket at startup: Bedrock goes through Geyser's
NetherNet transport, and 19132/udp is not open after boot. It is listed as
unboundPorts in that game's test.yaml, with the reason, until a Bedrock
client confirms how players reach it.

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

cmd/gbrgames/boottest.go

@@ -136,10 +136,20 @@ func bootTestPayload(gamesDir, id string, fillBlank bool) (map[string]any, error
 		}
 	}
 	// Once up, the server must listen on what nodes publish: the container side of every default port
+	// test.yaml's unboundPorts are published but only opened once a player connects; each is listed by
+	// hand, with the reason in a comment
+	unbound := map[string]bool{}
+	if list, ok := test["unboundPorts"].([]any); ok {
+		for _, p := range list {
+			unbound[fmt.Sprint(p)] = true
+		}
+	}
 	expectPorts := []any{}
 	if ports, ok := g["defaultPorts"].([]any); ok {
 		for _, p := range ports {
-			expectPorts = append(expectPorts, fmt.Sprint(p))
+			if !unbound[fmt.Sprint(p)] {
+				expectPorts = append(expectPorts, fmt.Sprint(p))
+			}
 		}
 	}