Implement engine-bridge v2 plugin masquerade (#10)

src/Recordingtest.EgPlugin/PortResolver.cs

@@ -0,0 +1,18 @@
+namespace Recordingtest.EgPlugin;
+
+public static class PortResolver
+{
+    public const int DefaultPort = 38080;
+    public const string EnvVarName = "RECORDINGTEST_BRIDGE_PORT";
+
+    public static int Resolve(Func<string, string?>? envReader = null)
+    {
+        envReader ??= Environment.GetEnvironmentVariable;
+        var raw = envReader(EnvVarName);
+        if (!string.IsNullOrWhiteSpace(raw) && int.TryParse(raw, out var p) && p > 0 && p < 65536)
+        {
+            return p;
+        }
+        return DefaultPort;
+    }
+}