Add share target, prompt templates, command palette and session organisation

- PWA share target: shared text/links start a new chat or go into a
  recent session (chooser dialog)
- Prompt templates (personal + global for admins) with {{placeholders}}
  that are asked for on insert; managed under Settings → Templates
- Ctrl/Cmd+K command palette; Alt+N new session, Alt+Up/Down switch
  sessions, Ctrl+, settings
- Sessions can be pinned, archived and filed into folders; the list can
  be grouped by date or by project, groups are collapsible
- Fix: the "What's new" dialog was never shown to signed-in users

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/App.tsx

@@ -16,6 +16,9 @@ import { Spinner, useTitleActivity } from "./components/Activity";
 import { DialogHost } from "./dialogs";
 import { startPrefsSync } from "./prefsSync";
 import { WhatsNew } from "./components/WhatsNew";
+import { ShareTarget } from "./components/ShareTarget";
+import { Palette } from "./components/Palette";
+import { pendingShare } from "./share";
 
 // The file manager (editor, git) is loaded on demand to keep the chat small.
 const Files = lazy(() => import("./components/Files").then((m) => ({ default: m.Files })));
@@ -27,6 +30,7 @@ export function App() {
   const [info, setInfo] = useState<Info>();
   const [error, setError] = useState<string>();
   const [menuOpen, setMenuOpen] = useState(false);
+  const [shared, setShared] = useState(pendingShare);
   useTitleActivity();
 
   const refresh = async () => {
@@ -71,7 +75,6 @@ export function App() {
       <>
         <Login info={info} onSuccess={refresh} />
         <DialogHost />
-      {info?.user && <WhatsNew version={info.version} />}
       </>
     );
 
@@ -101,6 +104,9 @@ export function App() {
       {menuOpen && <div className="backdrop" onClick={() => setMenuOpen(false)} />}
       <Sidebar open={menuOpen} activeId={section === "s" ? arg : undefined} section={section ?? ""} />
       <main className="main">{content}</main>
+      <WhatsNew version={info.version} />
+      <Palette />
+      {shared && <ShareTarget shared={shared} onClose={() => setShared(null)} />}
       <DialogHost />
     </div>
   );