feat: the assistant's chat slides open and shut, smaller on a computer, a screen of its own on a phone that «назад» closes; a sparkle button

internal/server/web/static/app.js

@@ -61,11 +61,15 @@
     $('main#app').dataset.view = view;
     document.dispatchEvent(new CustomEvent('app:view', {detail: view}));
   }
+  // The address the shell shows; a history step that keeps it (a chat on a
+  // phone closing by «назад») moves no view.
+  let shown = location.pathname + location.search;
   async function go(url, push = true) {
     const u = new URL(url, location.href);
     const view = viewOf(u.pathname);
     if (!view || u.origin !== location.origin) { location.href = u.href; return; }
     if (push && u.pathname + u.search !== location.pathname + location.search) history.pushState({}, '', u.pathname + u.search + u.hash);
+    shown = u.pathname + u.search;
     show(view);
     if (view !== 'terminal') await load($('.view[data-view="' + view + '"]'), u.pathname + u.search);
   }
@@ -77,7 +81,7 @@
     const u = new URL(a.href, location.href);
     if (u.origin === location.origin && viewOf(u.pathname)) { ev.preventDefault(); go(u.href); }
   });
-  window.addEventListener('popstate', () => go(location.href, false));
+  window.addEventListener('popstate', () => { if (location.pathname + location.search !== shown) go(location.href, false); });
 
   // A form in a fragment is sent from here: the answer's address says what
   // to draw. /logout and forms outside the views go the usual way; a form