feat(pwa): experimental — add my.dash.board virtual host for secure PWA install

Serve the dashboard over a local HTTPS virtual host (my.dash.board) so
Chrome treats it as a secure origin and shows the PWA install prompt.

- Add native-host/dashboard-server.js: bare-http1 static file server
  backed by bare-bundle assets in distribution mode, disk fallback in dev
- Add setLocalVirtualHost() to virtual-hosts.js; type:local entries are
  protected from removal and filtered out of saveState persistence
- Export setLocalVirtualHost from holesail-manager/index.js
- Start dashboard server in startup.js after proxies are ready and
  register my.dash.board as a local virtual host
- Stop dashboard server in message-router.js cleanup()
- Update manifest.webmanifest: start_url, id, scope → https://my.dash.board/
- Embed all extension/dashboard/ files as bare-bundle assets in
  build-distributable.js patchBundle() — no installer copy step needed
- Hide checkbox, hs:// URL, Reconnect, and Remove controls for built-in
  my.dash.board row in the virtual hosts table UI

native-host/holesail-manager/index.js

@@ -29,9 +29,9 @@ function saveState() {
   const serversList = serversModule.getServers().map(s => ({
     id: s.id, port: s.port, host: s.host, secure: s.secure, udp: s.udp || false, label: s.label || ''
   }));
-  const virtualHostsList = vhostsModule.getVirtualHosts().map(v => ({
-    hostname: v.hostname, hsUrl: v.hsUrl
-  }));
+  const virtualHostsList = vhostsModule.getVirtualHosts()
+    .filter(v => v.type !== 'local') // never persist built-in local hosts
+    .map(v => ({ hostname: v.hostname, hsUrl: v.hsUrl }));
   const serviceTunnelsList = svcModule.getServiceTunnels().map(t => ({
     id: t.id, label: t.label, hsUrl: t.hsUrl, localPort: t.localPort
   }));
@@ -125,6 +125,7 @@ module.exports = {
   getServers: serversModule.getServers,
   // Virtual hosts
   setVirtualHost: vhostsModule.setVirtualHost,
+  setLocalVirtualHost: vhostsModule.setLocalVirtualHost,
   removeVirtualHost: vhostsModule.removeVirtualHost,
   getVirtualHosts: vhostsModule.getVirtualHosts,
   getLocalPortForHostname: vhostsModule.getLocalPortForHostname,