add simple-host example

examples/simple-host/sandbox.html

@@ -0,0 +1,48 @@
+<!doctype html>
+<html>
+  <head>
+    <meta charset="utf-8" />
+    <!-- Permissive CSP so nested content is not constrained by host CSP -->
+    <meta http-equiv="Content-Security-Policy" content="
+      default-src 'self';
+      img-src * data: blob: 'unsafe-inline';
+      media-src * blob: data:;
+      font-src * blob: data:;
+      script-src 'self'
+                 'wasm-unsafe-eval'
+                 'unsafe-inline'
+                 'unsafe-eval'
+                 blob: data: http://localhost:* https://localhost:*;
+      style-src * blob: data: 'unsafe-inline';
+      connect-src *;
+      frame-src * blob: data: http://localhost:* https://localhost:*;
+      base-uri 'self';
+    " />
+    <title>MCP-UI Proxy</title>
+    <style>
+      html,
+      body {
+        margin: 0;
+        height: 100vh;
+        width: 100vw;
+      }
+      body {
+        display: flex;
+        flex-direction: column;
+      }
+      * {
+        box-sizing: border-box;
+      }
+      iframe {
+        background-color: transparent;
+        border: 0px none transparent;
+        padding: 0px;
+        overflow: hidden;
+        flex-grow: 1;
+      }
+    </style>
+  </head>
+  <body>
+    <script type="module" src="/src/sandbox.ts"></script>
+  </body>
+</html>