Add standalone POC comparing WebRTC DataChannel vs Socket.IO

Self-contained test under poc-webrtc/ that does not touch the game.
Spins up an Express + WebSocket signaling + node-datachannel server
alongside a Socket.IO server, serves a simple browser client that
runs the same game-like traffic pattern (14Hz worldUpdates, input
events, ping/pong) over either transport based on a URL flag.

Captures per-session stats to a JSONL file and ships an analyze.js
that prints a per-(transport, phase) summary of RTT percentiles,
receive rate, and seq-gap counts so the TCP-vs-UDP-style comparison
becomes quantitative rather than eyeball.

Confirms node-datachannel installs and works on this platform and
that the dual-channel (reliable + unreliable) pattern is feasible
to maintain — both prerequisites for the real integration.

poc-webrtc/public/socketio-client.js

@@ -0,0 +1,20 @@
+// Socket.IO comparison client. Uses the same POC.attach() / POC.handleMessage()
+// interface as the WebRTC client so the comparison is apples-to-apples.
+
+(function () {
+    const POC = window.POC;
+    POC.setStatus("connecting (socketio)…", "wait");
+
+    const sock = io({ path: "/socketio" });
+    sock.on("connect", () => {
+        POC.log("socket.io connected " + sock.id);
+        POC.setStatus("connected (socket.io)", "ok");
+        POC.attach((obj) => sock.emit("msg", obj));
+    });
+    sock.on("disconnect", () => {
+        POC.log("socket.io disconnected");
+        POC.setStatus("disconnected", "bad");
+    });
+    sock.on("connect_error", (err) => POC.log("socket.io error: " + err.message));
+    sock.on("msg", (data) => POC.handleMessage(data));
+})();