feat: add rule dispatch, cross-plugin API, and Docker integration test

Wire rule registry and authenticated callbacks into both client and server
runtimes; expose __yonexusClient / __yonexusServer on globalThis for
cross-plugin communication. Add Docker-based integration test with
server-test-plugin (test_ping echo) and client-test-plugin (test_pong
receiver), plus docker-compose setup. Fix transport race condition where
a stale _connections entry caused promoteToAuthenticated to silently fail.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/docker/docker-compose.yml

@@ -0,0 +1,46 @@
+services:
+  yonexus-server:
+    build:
+      context: ../..
+      dockerfile: tests/docker/server/Dockerfile
+    environment:
+      # Identifier the client will use — must match IDENTIFIER on the client side
+      CLIENT_IDENTIFIER: test-client
+      # Required: Discord bot token and admin user ID for pairing notifications
+      NOTIFY_BOT_TOKEN: ${NOTIFY_BOT_TOKEN}
+      ADMIN_USER_ID: ${ADMIN_USER_ID}
+      # Optional: override the publicWsUrl advertised to clients
+      # PUBLIC_WS_URL: ws://yonexus-server:8787
+    networks:
+      - yonexus-net
+    healthcheck:
+      # Wait until the Yonexus WebSocket port is accepting connections
+      test:
+        - CMD
+        - node
+        - -e
+        - "require('net').createConnection({port:8787,host:'127.0.0.1'}).on('connect',()=>process.exit(0)).on('error',()=>process.exit(1))"
+      interval: 5s
+      timeout: 3s
+      retries: 12
+      start_period: 15s
+
+  yonexus-client:
+    build:
+      context: ../..
+      dockerfile: tests/docker/client/Dockerfile
+    environment:
+      # Must match CLIENT_IDENTIFIER on the server side
+      IDENTIFIER: test-client
+      NOTIFY_BOT_TOKEN: ${NOTIFY_BOT_TOKEN}
+      ADMIN_USER_ID: ${ADMIN_USER_ID}
+      YONEXUS_SERVER_URL: ws://yonexus-server:8787
+    networks:
+      - yonexus-net
+    depends_on:
+      yonexus-server:
+        condition: service_healthy
+
+networks:
+  yonexus-net:
+    driver: bridge