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/lib/tapconfirm.test.ts

@@ -0,0 +1,66 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { createTapConfirm } from './tapconfirm';
+
+describe('createTapConfirm', () => {
+  beforeEach(() => vi.useFakeTimers());
+  afterEach(() => vi.useRealTimers());
+
+  it('arms a window and reverts after the duration', () => {
+    const changes: boolean[] = [];
+    const c = createTapConfirm({ durationMs: 2000, onConfirm: () => {}, onChange: (x) => changes.push(x) });
+    c.arm();
+    expect(c.confirming).toBe(true);
+    expect(changes).toEqual([true]);
+    vi.advanceTimersByTime(1999);
+    expect(c.confirming).toBe(true);
+    vi.advanceTimersByTime(1);
+    expect(c.confirming).toBe(false);
+    expect(changes).toEqual([true, false]);
+  });
+
+  it('confirms within the window exactly once and stops the revert timer', () => {
+    const onConfirm = vi.fn();
+    const c = createTapConfirm({ durationMs: 2000, onConfirm });
+    c.arm();
+    c.confirm();
+    expect(onConfirm).toHaveBeenCalledTimes(1);
+    expect(c.confirming).toBe(false);
+    vi.advanceTimersByTime(5000); // the revert timer must not fire after a confirm
+    expect(onConfirm).toHaveBeenCalledTimes(1);
+  });
+
+  it('ignores confirm when the window is not open', () => {
+    const onConfirm = vi.fn();
+    const c = createTapConfirm({ durationMs: 2000, onConfirm });
+    c.confirm();
+    expect(onConfirm).not.toHaveBeenCalled();
+    expect(c.confirming).toBe(false);
+  });
+
+  it('treats arm as idempotent while already confirming', () => {
+    const changes: boolean[] = [];
+    const c = createTapConfirm({ durationMs: 2000, onConfirm: () => {}, onChange: (x) => changes.push(x) });
+    c.arm();
+    c.arm();
+    expect(changes).toEqual([true]);
+  });
+
+  it('cancel closes the window without confirming', () => {
+    const onConfirm = vi.fn();
+    const c = createTapConfirm({ durationMs: 2000, onConfirm });
+    c.arm();
+    c.cancel();
+    expect(c.confirming).toBe(false);
+    vi.advanceTimersByTime(5000);
+    expect(onConfirm).not.toHaveBeenCalled();
+  });
+
+  it('dispose clears a pending timer without a revert callback', () => {
+    const changes: boolean[] = [];
+    const c = createTapConfirm({ durationMs: 2000, onConfirm: () => {}, onChange: (x) => changes.push(x) });
+    c.arm();
+    c.dispose();
+    vi.advanceTimersByTime(5000);
+    expect(changes).toEqual([true]);
+  });
+});