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.ts

@@ -0,0 +1,79 @@
+/**
+ * tapconfirm holds the small state machine behind the "tap to confirm" controls: the
+ * first tap arms a confirmation window of durationMs (during which the view shows a
+ * fading ✅), a second tap within it confirms, and otherwise the window reverts. It is
+ * framework agnostic — a view observes onChange and renders accordingly — so the timing
+ * logic is unit-testable without a DOM. The pending timer is the only side effect.
+ */
+export interface TapConfirmOptions {
+  /** Length of the confirmation window in milliseconds. */
+  durationMs: number;
+  /** Invoked once when a confirmation lands inside the window. */
+  onConfirm: () => void;
+  /** Invoked whenever the confirming flag flips, so a view can react. */
+  onChange?: (confirming: boolean) => void;
+}
+
+/** TapConfirmController drives a single "tap to confirm" control. */
+export interface TapConfirmController {
+  /** Whether the confirmation window is currently open. */
+  readonly confirming: boolean;
+  /** Arm the confirmation window; a no-op while it is already open. */
+  arm(): void;
+  /** Confirm within the window: fires onConfirm once and closes the window. A no-op
+   *  while the window is closed. */
+  confirm(): void;
+  /** Close the window without confirming (e.g. the control was disabled). */
+  cancel(): void;
+  /** Clear any pending timer; the controller must not be reused afterwards. */
+  dispose(): void;
+}
+
+/**
+ * createTapConfirm builds a TapConfirmController whose confirmation window lasts
+ * durationMs. onConfirm fires once per confirmed window; onChange (when given)
+ * reports every flip of the confirming flag.
+ */
+export function createTapConfirm(opts: TapConfirmOptions): TapConfirmController {
+  let confirming = false;
+  let timer: ReturnType<typeof setTimeout> | null = null;
+
+  function clear(): void {
+    if (timer !== null) {
+      clearTimeout(timer);
+      timer = null;
+    }
+  }
+  function set(next: boolean): void {
+    if (confirming === next) return;
+    confirming = next;
+    opts.onChange?.(next);
+  }
+  return {
+    get confirming() {
+      return confirming;
+    },
+    arm() {
+      if (confirming) return;
+      set(true);
+      timer = setTimeout(() => {
+        timer = null;
+        set(false);
+      }, opts.durationMs);
+    },
+    confirm() {
+      if (!confirming) return;
+      clear();
+      set(false);
+      opts.onConfirm();
+    },
+    cancel() {
+      if (!confirming) return;
+      clear();
+      set(false);
+    },
+    dispose() {
+      clear();
+    },
+  };
+}