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/components/Screen.svelte

@@ -10,7 +10,6 @@
   let {
     title,
     back,
-    menu,
     tabbar,
     children,
     scroll = true,
@@ -19,7 +18,6 @@
   }: {
     title: string;
     back?: string;
-    menu?: Snippet;
     tabbar?: Snippet;
     children?: Snippet;
     scroll?: boolean;
@@ -58,7 +56,7 @@
 </script>
 
 <div class="screen">
-  <Header {title} {back} {menu} grow={growNav} />
+  <Header {title} {back} grow={growNav} />
   {#if SHOW_AD_BANNER}<AdBanner />{/if}
   <main class="content" class:scroll class:fill={!growNav} class:column>{@render children?.()}</main>
   {#if tabbar}