feat(dave): pass arbiter gate 1 — selfbot joins DAVE/MLS E2EE voice group

Fail-fast checkpoint the arbiter mandated before committing to option A
(protocol-level selfbot stream receive). dave/gate.mjs proves, live against
Discord, that a user token can pass the voice DAVE/MLS handshake:

- voice GW v8 IDENTIFY with max_dave_protocol_version=1 -> NO close 4017
- dave_protocol_version=1 negotiated (E2EE active on the channel)
- @snazzah/davey drives full MLS membership: op25 external_sender -> op26
  key_package -> op27 proposals -> op28 commit_welcome -> op29 announce_commit
  -> MLS session ready=true, stable 5s, voicePrivacyCode derived

Confirms option A is viable: the selfbot can join the E2EE group as a full
member, which is the prerequisite for receiving+decrypting the video RTP.
PLAN.md updated with gate result, exact binary framing, and next A steps.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

dave/package.json

@@ -0,0 +1,10 @@
+{
+  "name": "wsai-dave-poc",
+  "private": true,
+  "type": "module",
+  "description": "Fail-fast gate: can a selfbot pass the Discord voice DAVE/MLS (close 4017) handshake?",
+  "dependencies": {
+    "ws": "^8.18.0",
+    "@snazzah/davey": "^0.1.12"
+  }
+}