UI: tab-bar navigation — drop the hamburger

Replace Menu.svelte (hamburger) everywhere with tab-bar navigation:
- Settings hub (SettingsHub) from the lobby ⚙️ tab: Settings/Profile/
  Friends/About as in-place tabs, back → lobby; the lobby ⚙️ badge counts
  incoming friend requests (invitations keep their own lobby section).
- Comms hub (CommsHub) from the move-history 💬: Chat/Dictionary tabs,
  back → game; Dictionary only while the game is active.
- Game menu items relocate into the open history: 🏁 leave / 📤 export in
  the header, 🤝 add-friend per opponent card, 💬 comms; unread chat is
  badged on the score bar + the 💬.
- TapConfirm (tap → fading ✅ → tap) replaces the Skip/Hint press-and-hold
  popovers and drives the add-friend confirm.
- Fix the move-history "jump": the slid board is inert and the stage can't
  scroll, so a swipe up genuinely closes the history.

Remove Menu.svelte + HoldConfirm.svelte. Docs: UI_DESIGN, FUNCTIONAL(+ru),
PRERELEASE. UI check/unit/build/bundle/e2e (Chromium+WebKit) all green.

ui/src/App.svelte

@@ -9,14 +9,10 @@
   import Login from './screens/Login.svelte';
   import Lobby from './screens/Lobby.svelte';
   import NewGame from './screens/NewGame.svelte';
-  import Profile from './screens/Profile.svelte';
-  import Settings from './screens/Settings.svelte';
-  import About from './screens/About.svelte';
-  import Friends from './screens/Friends.svelte';
+  import SettingsHub from './screens/SettingsHub.svelte';
   import Stats from './screens/Stats.svelte';
   import Game from './game/Game.svelte';
-  import ChatScreen from './game/ChatScreen.svelte';
-  import CheckScreen from './game/CheckScreen.svelte';
+  import CommsHub from './game/CommsHub.svelte';
 
   onMount(() => {
     void bootstrap();
@@ -83,17 +79,17 @@
         {:else if router.route.name === 'game'}
           <Game id={router.route.params.id} />
         {:else if router.route.name === 'gameChat'}
-          <ChatScreen id={router.route.params.id} />
+          <CommsHub id={router.route.params.id} initialTab="chat" />
         {:else if router.route.name === 'gameCheck'}
-          <CheckScreen id={router.route.params.id} />
+          <CommsHub id={router.route.params.id} initialTab="dictionary" />
         {:else if router.route.name === 'profile'}
-          <Profile />
+          <SettingsHub initialTab="profile" />
         {:else if router.route.name === 'settings'}
-          <Settings />
+          <SettingsHub initialTab="settings" />
         {:else if router.route.name === 'about'}
-          <About />
+          <SettingsHub initialTab="about" />
         {:else if router.route.name === 'friends'}
-          <Friends />
+          <SettingsHub initialTab="friends" />
         {:else if router.route.name === 'stats'}
           <Stats />
         {:else}