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

extension/dashboard/pages/virtual-hosts.js

@@ -54,18 +54,23 @@ function updateConnectionsTable(state) {
     const openUrl = `https://${hostname}`;
     const safeHostname = hostname.replace(/"/g, '"');
     const needsReconnect = v.state === 'error' || v.state === 'closed';
+    const isBuiltIn = v.type === 'local';
     return `
       <tr>
-        <td style="width:32px;"><input type="checkbox" class="vhost-row-cb" data-hostname="${safeHostname}"></td>
-        <td><span class="mono-chip">${escapeHtml(hostname)}</span></td>
+        <td style="width:32px;">${isBuiltIn ? '' : `<input type="checkbox" class="vhost-row-cb" data-hostname="${safeHostname}">`}</td>
         <td>
+          <span class="mono-chip">${escapeHtml(hostname)}</span>
+          ${isBuiltIn ? '<span style="font-size:10px;color:var(--text4);margin-left:4px;">built-in</span>' : ''}
+        </td>
+        <td>
+          ${isBuiltIn ? '<span style="color:var(--text4);font-size:11px;">—</span>' : `
           <div style="display:flex;align-items:center;gap:6px;">
             <span class="mono" title="${escapeHtml(hsUrl)}" style="color:var(--text3);font-size:11px;">${truncate(hsUrl, 28)}</span>
             <button class="btn-icon copy-btn" data-copy="${escapeHtml(hsUrl)}" title="Copy hs:// URL" style="flex-shrink:0;">
               <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><rect x="9" y="9" width="13" height="13" rx="2"/><path d="M5 15H4a2 2 0 0 1-2-2V4a2 2 0 0 1 2-2h9a2 2 0 0 1 2 2v1"/></svg>
               <span class="copy-tooltip">Copied!</span>
             </button>
-          </div>
+          </div>`}
         </td>
         <td class="mono" style="font-size:11px;color:var(--text3);">${escapeHtml(backend)}</td>
         <td>
@@ -78,14 +83,14 @@ function updateConnectionsTable(state) {
               <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M18 13v6a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2V8a2 2 0 0 1 2-2h6"/><polyline points="15,3 21,3 21,9"/><line x1="10" y1="14" x2="21" y2="3"/></svg>
               Open
             </a>
-            ${needsReconnect ? `<button class="btn btn-secondary btn-sm" data-reconnect-vhost="${safeHostname}" data-hs-url="${escapeHtml(hsUrl)}" title="Reconnect tunnel">
+            ${!isBuiltIn && needsReconnect ? `<button class="btn btn-secondary btn-sm" data-reconnect-vhost="${safeHostname}" data-hs-url="${escapeHtml(hsUrl)}" title="Reconnect tunnel">
               <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><polyline points="23,4 23,10 17,10"/><path d="M20.49 15a9 9 0 1 1-.07-8.13"/></svg>
               Reconnect
             </button>` : ''}
-            <button class="btn btn-danger btn-sm" data-remove-vhost="${safeHostname}">
+            ${isBuiltIn ? '' : `<button class="btn btn-danger btn-sm" data-remove-vhost="${safeHostname}">
               <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><polyline points="3,6 5,6 21,6"/><path d="M19,6l-1,14a2,2,0,0,1-2,2H8a2,2,0,0,1-2-2L5,6"/></svg>
               Remove
-            </button>
+            </button>`}
           </div>
         </td>
       </tr>`;