feat(host): wire techdemo host capability flow

Route browser/PWA share and native-shell haptic host results through techdemo app code before returning normal hemx effects; serve the tiny browser host adapter as an app asset.

req: host/001

req: host/002

req: host/004

req: host/005

req: examples/001

examples/techdemo/templates/app_shell.heml

@@ -5,6 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <title>hemx Techdemo</title>
   <script +src="self.runtime_src" defer></script>
+  <script src="/hemx-browser-host.js" defer></script>
   <script src="/island.js" defer></script>
   <link rel="stylesheet" href="/app.css">
   <link rel="stylesheet" href="/control_center.css">