Add WebSocket bug demo project

websocket-bug-demo/.gitignore

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+node_modules/

websocket-bug-demo/Dockerfile

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+FROM node:20-alpine
+
+WORKDIR /app
+
+COPY package*.json ./
+RUN npm install
+
+COPY . .
+
+EXPOSE 7654 6543
+
+CMD ["node", "server.js"]

websocket-bug-demo/README.md

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+# WebSocket Bug Demo
+
+A demo project to reproduce a WebSocket connection bug in Zen browser.
+
+## The Bug
+
+When opening a web app served from `localhost:7654` and attempting to connect to a WebSocket server on `localhost:6543` (different port), the connection gets blocked by the browser.
+
+This issue appears to originate from Zen browser's Advanced Tracking Protection functionality, though the exact cause is still uncertain.
+
+## Quick Start
+
+### Option 1: Docker (recommended)
+
+```bash
+docker compose up --build
+```
+
+### Option 2: Local
+
+```bash
+npm install
+npm start
+```
+
+## Usage
+
+Open http://localhost:7654 in your browser and click "Connect".
+
+- **HTTP server**: `localhost:7654` - serves the client UI
+- **WebSocket server**: `localhost:6543` - sends pings every 5 seconds

websocket-bug-demo/docker-compose.yml

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+services:
+  websocket-demo:
+    build: .
+    ports:
+      - "7654:7654"
+      - "6543:6543"
+    restart: unless-stopped