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/screens/SettingsHub.svelte

@@ -0,0 +1,64 @@
+<script lang="ts">
+  import Screen from '../components/Screen.svelte';
+  import TabBar from '../components/TabBar.svelte';
+  import Settings from './Settings.svelte';
+  import Profile from './Profile.svelte';
+  import Friends from './Friends.svelte';
+  import About from './About.svelte';
+  import { app } from '../lib/app.svelte';
+  import { t, type MessageKey } from '../lib/i18n/index.svelte';
+
+  // The Settings hub: a single nav bar + bottom tab bar hosting the Settings / Profile /
+  // Friends / About bodies. Tabs switch in place (no navigation), so the back control
+  // always returns to the lobby. Guests have no social surface, so the Friends tab hides.
+  type SettingsTab = 'settings' | 'profile' | 'friends' | 'about';
+  let { initialTab = 'settings' }: { initialTab?: SettingsTab } = $props();
+
+  const guest = $derived(app.profile?.isGuest ?? true);
+  // The active tab is seeded once from the entry route's tab and then owned locally;
+  // the hub is keyed by route in App.svelte, so initialTab is constant for its lifetime.
+  // svelte-ignore state_referenced_locally
+  let tab = $state<SettingsTab>(initialTab);
+  // A guest who deep-links to the Friends tab falls back to Settings.
+  $effect(() => {
+    if (guest && tab === 'friends') tab = 'settings';
+  });
+
+  const titleKey: Record<SettingsTab, MessageKey> = {
+    settings: 'settings.title',
+    profile: 'profile.title',
+    friends: 'friends.title',
+    about: 'about.title',
+  };
+</script>
+
+<Screen title={t(titleKey[tab])} back="/">
+  {#if tab === 'settings'}
+    <Settings />
+  {:else if tab === 'profile'}
+    <Profile />
+  {:else if tab === 'friends'}
+    <Friends />
+  {:else}
+    <About />
+  {/if}
+
+  {#snippet tabbar()}
+    <TabBar>
+      <button class="tab" class:active={tab === 'settings'} onclick={() => (tab = 'settings')} aria-label={t('settings.title')}>
+        <span class="sq">⚙️</span>
+      </button>
+      <button class="tab" class:active={tab === 'profile'} onclick={() => (tab = 'profile')} aria-label={t('profile.title')}>
+        <span class="sq">👤</span>
+      </button>
+      {#if !guest}
+        <button class="tab" class:active={tab === 'friends'} onclick={() => (tab = 'friends')} aria-label={t('friends.title')}>
+          <span class="sq">🤝{#if app.notifications > 0}<span class="badge">{app.notifications}</span>{/if}</span>
+        </button>
+      {/if}
+      <button class="tab" class:active={tab === 'about'} onclick={() => (tab = 'about')} aria-label={t('about.title')}>
+        <span class="sq">ℹ️</span>
+      </button>
+    </TabBar>
+  {/snippet}
+</Screen>