feat(web): add web demo and polish Lit web components UI and demo tooling

demo/build.web.ts

@@ -0,0 +1,41 @@
+import * as esbuild from 'esbuild';
+
+// Shim unused Node.js built-ins that get pulled in by dependencies.
+const nodeShimPlugin: esbuild.Plugin = {
+  name: 'node-builtins-shim',
+  setup(build) {
+    // Mark node built-ins as empty modules — they are imported but not actually used at runtime.
+    const builtins = ['path', 'fs', 'os', 'crypto', 'stream', 'util', 'events', 'http', 'https', 'net', 'tls', 'child_process', 'url', 'assert', 'buffer', 'tty', 'readline'];
+    const filter = new RegExp(`^(${builtins.join('|')})$`);
+    build.onResolve({ filter }, (args) => ({
+      path: args.path,
+      namespace: 'node-shim',
+    }));
+    build.onLoad({ filter: /.*/, namespace: 'node-shim' }, () => ({
+      contents: 'export default {};',
+      loader: 'js',
+    }));
+  },
+};
+
+const buildOptions: esbuild.BuildOptions = {
+  entryPoints: ['demo/demo.web.ts'],
+  bundle: true,
+  format: 'esm',
+  platform: 'browser',
+  outdir: 'demo',
+  sourcemap: true,
+  target: 'es2022',
+  logLevel: 'info',
+  plugins: [nodeShimPlugin],
+};
+
+const serve = process.argv.includes('--serve');
+
+if (serve) {
+  const ctx = await esbuild.context(buildOptions);
+  const { host, port } = await ctx.serve({ servedir: 'demo' });
+  console.log(`\n  🌐 Web demo running at http://localhost:${port}/demo.web.html\n`);
+} else {
+  await esbuild.build(buildOptions);
+}