spike: minimal N-API libdatachannel binding — WebRTC handshake proven

Phase 0 of GoLive rewrite (drop @dank074/node-datachannel 771MB):
minimal N-API binding exposing PeerConnection/DataChannel/ICE/SDP,
built against libdatachannel 0.24.0 (from node-datachannel _deps source).

Verified: offer/answer/ICE/DataChannel roundtrip between two local
peers (test-handshake.js). Key findings:
- callbacks must be registered in ctor BEFORE createDataChannel
- SDP with candidates comes from localDescription() at gathering Complete
- answer auto-generates on setRemoteDescription(offer); do NOT call
  setLocalDescription() after or role=actpass breaks the peer

services/discord-gateway/native/libdatachannel-min/binding.gyp

@@ -0,0 +1,21 @@
+{
+  "targets": [
+    {
+      "target_name": "libdatachannel_min",
+      "sources": ["binding.cpp"],
+      "include_dirs": [
+        "<!@(node -p \"require('node-addon-api').include\")",
+        "/home/code/GMW/services/discord-gateway/node_modules/.pnpm/@lng2004+node-datachannel@0.32.0-20260202/node_modules/@lng2004/node-datachannel/build/_deps/libdatachannel-src/include"
+      ],
+      "libraries": [
+        "/tmp/ldc-build/libdatachannel.so.0.24.0"
+      ],
+      "cflags": ["-std=c++17", "-fexceptions"],
+      "cflags_cc": ["-std=c++17", "-fexceptions"],
+      "defines": ["NAPI_CPP_EXCEPTIONS"],
+      "conditions": [
+        ["OS=='linux'", { "cflags": ["-fvisibility=hidden"] }]
+      ]
+    }
+  ]
+}