Add compose demo app for VeilStream preview testing

web (node) renders the seeded customers table plus container hostname.
db (postgres:16-alpine) seeds five PII-shaped rows from db/init.sql.

.gitignore

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+TOS.txt
+node_modules/

README.md

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+# veilstream-demo
+
+Throwaway app for testing VeilStream preview environments.
+
+Two services:
+
+- `web` - Node, no framework. Renders the `customers` table plus the container
+  hostname, so you can tell one preview environment from another.
+- `db` - `postgres:16-alpine`, seeded from `db/init.sql` with five rows of
+  deliberately PII-shaped data (name, email, phone) to give the sanitization
+  features something to act on.
+
+Primary service is `web` on port 3000. `/healthz` returns `ok`.
+
+Run locally:
+
+    docker compose up --build
+
+Then open
+
+http://localhost:3000

db/init.sql

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+CREATE TABLE customers (
+  id         serial PRIMARY KEY,
+  full_name  text NOT NULL,
+  email      text NOT NULL,
+  phone      text NOT NULL,
+  city       text NOT NULL,
+  plan       text NOT NULL,
+  mrr_cents  integer NOT NULL
+);
+
+INSERT INTO customers (full_name, email, phone, city, plan, mrr_cents) VALUES
+  ('Ada Lovelace',    'ada@example.com',    '+1 250 555 0101', 'Victoria',  'pro',        9900),
+  ('Grace Hopper',    'grace@example.com',  '+1 250 555 0102', 'Nanaimo',   'team',      29900),
+  ('Alan Turing',     'alan@example.com',   '+1 604 555 0103', 'Vancouver', 'free',          0),
+  ('Katherine Johnson','kj@example.com',    '+1 250 555 0104', 'Sidney',    'pro',        9900),
+  ('Edsger Dijkstra', 'edsger@example.com', '+1 778 555 0105', 'Victoria',  'enterprise',99900);

docker-compose.yml

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+services:
+  web:
+    build:
+      context: ./web
+    ports:
+      - "3000:3000"
+    environment:
+      DATABASE_URL: postgres://demo:demo@db:5432/demo
+      APP_LABEL: "VeilStream demo"
+    depends_on:
+      db:
+        condition: service_healthy
+
+  db:
+    image: postgres:16-alpine
+    environment:
+      POSTGRES_USER: demo
+      POSTGRES_PASSWORD: demo
+      POSTGRES_DB: demo
+    volumes:
+      - ./db/init.sql:/docker-entrypoint-initdb.d/init.sql
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U demo -d demo"]
+      interval: 5s
+      timeout: 3s
+      retries: 20

web/Dockerfile

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+FROM node:20-alpine
+WORKDIR /app
+COPY package.json ./
+RUN npm install --omit=dev
+COPY server.js ./
+EXPOSE 3000
+CMD ["node", "server.js"]

web/package.json

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+{
+  "name": "veilstream-demo-web",
+  "version": "1.0.0",
+  "private": true,
+  "main": "server.js",
+  "dependencies": {
+    "pg": "^8.13.1"
+  }
+}

web/server.js

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+const http = require("http");
+const os = require("os");
+const { Pool } = require("pg");
+
+const pool = new Pool({ connectionString: process.env.DATABASE_URL });
+const label = process.env.APP_LABEL || "VeilStream demo";
+const port = Number(process.env.PORT || 3000);
+
+const esc = (s) =>
+  String(s).replace(/[&<>"]/g, (c) => ({ "&": "&amp;", "<": "&lt;", ">": "&gt;", '"': "&quot;" }[c]));
+
+async function page() {
+  let rows = [];
+  let dbError = null;
+  try {
+    const r = await pool.query(
+      "SELECT id, full_name, email, phone, city, plan, mrr_cents FROM customers ORDER BY id"
+    );
+    rows = r.rows;
+  } catch (err) {
+    dbError = err.message;
+  }
+
+  const body = dbError
+    ? `<p class="err">Database unreachable: ${esc(dbError)}</p>`
+    : `<table>
+  <tr><th>id</th><th>name</th><th>email</th><th>phone</th><th>city</th><th>plan</th><th>mrr</th></tr>
+  ${rows
+    .map(
+      (r) =>
+        `<tr><td>${r.id}</td><td>${esc(r.full_name)}</td><td>${esc(r.email)}</td><td>${esc(
+          r.phone
+        )}</td><td>${esc(r.city)}</td><td>${esc(r.plan)}</td><td>$${(r.mrr_cents / 100).toFixed(
+          2
+        )}</td></tr>`
+    )
+    .join("\n  ")}
+</table>
+<p class="meta">${rows.length} rows. If these values look like real people, the seed was not sanitized.</p>`;
+
+  return `<!doctype html>
+<html><head><meta charset="utf-8"><title>${esc(label)}</title>
+<style>
+ body{font:15px/1.5 -apple-system,system-ui,sans-serif;margin:2rem auto;max-width:52rem;padding:0 1rem}
+ table{border-collapse:collapse;width:100%;margin:1rem 0}
+ th,td{border:1px solid #ccc;padding:.4rem .6rem;text-align:left}
+ th{background:#f4f4f4}
+ .meta{color:#666}
+ .err{color:#b00}
+ dl{display:grid;grid-template-columns:max-content 1fr;gap:.2rem 1rem}
+ dt{color:#666}
+</style></head><body>
+<h1>${esc(label)}</h1>
+<dl>
+ <dt>hostname</dt><dd>${esc(os.hostname())}</dd>
+ <dt>served at</dt><dd>${new Date().toISOString()}</dd>
+ <dt>node</dt><dd>${esc(process.version)}</dd>
+</dl>
+${body}
+</body></html>`;
+}
+
+http
+  .createServer(async (req, res) => {
+    if (req.url === "/healthz") {
+      res.writeHead(200, { "content-type": "text/plain" });
+      return res.end("ok\n");
+    }
+    res.writeHead(200, { "content-type": "text/html; charset=utf-8" });
+    res.end(await page());
+  })
+  .listen(port, "0.0.0.0", () => console.log(`listening on ${port}`));