Add playground backend and proxy

playground/nginx_container/html/502.json

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+{
+  "status": 502,
+  "error": "bad_gateway",
+  "message": "The requested Artemis session container or Cuttlefish device is provisioning, booting, or currently unreachable. Please retry shortly.",
+  "timestamp": "auto"
+}

playground/nginx_container/html/504.json

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+{
+  "status": 504,
+  "error": "gateway_timeout",
+  "message": "The upstream Artemis container or device service took too long to respond.",
+  "timestamp": "auto"
+}

playground/nginx_container/html/index.html

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+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  <title>Artemis Reverse Proxy</title>
+  <style>
+    body {
+      font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
+      background: #0f172a;
+      color: #f8fafc;
+      display: flex;
+      flex-direction: column;
+      align-items: center;
+      justify-content: center;
+      min-height: 100vh;
+      margin: 0;
+      padding: 20px;
+      box-sizing: border-box;
+    }
+    .card {
+      background: #1e293b;
+      border: 1px solid #334155;
+      border-radius: 16px;
+      padding: 40px;
+      max-width: 540px;
+      width: 100%;
+      box-shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.4);
+      text-align: center;
+    }
+    h1 {
+      font-size: 24px;
+      margin-bottom: 12px;
+      color: #38bdf8;
+    }
+    p {
+      color: #94a3b8;
+      font-size: 15px;
+      line-height: 1.6;
+    }
+    .status {
+      display: inline-flex;
+      align-items: center;
+      gap: 8px;
+      padding: 6px 14px;
+      background: #064e3b;
+      color: #34d399;
+      border-radius: 9999px;
+      font-size: 13px;
+      font-weight: 600;
+      margin-bottom: 20px;
+    }
+    .dot {
+      width: 8px;
+      height: 8px;
+      background: #10b981;
+      border-radius: 50%;
+    }
+  </style>
+</head>
+<body>
+  <div class="card">
+    <div class="status">
+      <span class="dot"></span> Ingress Proxy Active
+    </div>
+    <h1>Artemis Cloud Platform</h1>
+    <p>The reverse proxy is operational and listening on ports 80 &amp; 443. Connect your backend service to begin routing user sessions and Cuttlefish devices.</p>
+  </div>
+</body>
+</html>