Add the Sandbar mobile companion PWA

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

scripts/serve.mjs

@@ -0,0 +1,23 @@
+// Serves public/ on http://localhost:5173 for working on the app without a Sandbar-hosted copy.
+// The app then needs the server's address, and the server must allow this origin:
+//   SANDBAR_APP_ORIGIN=http://localhost:5173
+import { createServer } from 'node:http';
+import { readFile } from 'node:fs/promises';
+import { extname, join, normalize } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const root = fileURLToPath(new URL('../public/', import.meta.url));
+const types = { '.html': 'text/html', '.js': 'text/javascript', '.css': 'text/css', '.svg': 'image/svg+xml', '.png': 'image/png', '.webmanifest': 'application/manifest+json' };
+const port = Number(process.env.PORT || 5173);
+
+createServer(async (req, res) => {
+  let p = normalize(decodeURIComponent(new URL(req.url, 'http://x').pathname)).replace(/^([/\])+/, '');
+  if (p === '' || p.endsWith('/')) p += 'index.html';
+  if (p.includes('..')) { res.writeHead(400).end(); return; }
+  try {
+    const body = await readFile(join(root, p));
+    res.writeHead(200, { 'Content-Type': types[extname(p)] || 'application/octet-stream', 'Cache-Control': 'no-cache' }).end(body);
+  } catch {
+    res.writeHead(404).end('not found');
+  }
+}).listen(port, () => console.log(`http://localhost:${port}`));