fix(ui): mobile in-app WebView polish (tap-flash, VK haptics, swipe-back)

- Tap-highlight: add -webkit-tap-highlight-color: transparent on #app.
  Android in-app WebViews (Telegram, VK) flashed a momentary selection-like
  box on tappable nodes on tap — seen on the header title and the back
  chevron; user-select (already none) does not govern it. Inherited, so
  this clears it app-wide.

- VK haptics: mirror the Telegram haptic set on VK via VK Bridge taptic
  (impact / notification / selection), routed through a new shared
  lib/haptics.ts dispatcher. VK users previously got no haptics; the game
  and error call sites now fire haptic() instead of telegramHaptic().

- VK swipe-back: disable VK's horizontal swipe-back at launch
  (VKWebAppSetSwipeSettings history:false) so it does not fight the app's
  own edge-swipe-back and on-board tile drag — parity with Telegram's
  disabled vertical swipes; the app owns navigation via its back chevron.

Docs: UI_DESIGN (no-select / tap-highlight, VK integration).

ui/src/lib/vk.ts

@@ -6,6 +6,8 @@
 // (VKWebAppGetUserInfo, since VK omits it from the signed launch params). Every helper is safe to
 // call outside VK.
 
+import type { Haptic } from './telegram';
+
 async function bridge() {
   return (await import('@vkontakte/vk-bridge')).default;
 }
@@ -160,3 +162,39 @@ export async function vkOnInsets(handler: (insets: VKInsets) => void): Promise<v
     // Outside VK / bridge unavailable: the CSS env() safe-area fallback applies.
   }
 }
+
+/**
+ * vkHaptic fires a VK Bridge haptic mirroring the Telegram set: a selection tick
+ * (VKWebAppTapticSelectionChanged), a success/warning/error notification
+ * (VKWebAppTapticNotificationOccurred) or a light/medium/heavy impact (VKWebAppTapticImpactOccurred).
+ * Best-effort and a no-op outside VK or on a client without taptic support (the send rejects and is
+ * swallowed), so callers fire it unconditionally.
+ */
+export async function vkHaptic(kind: Haptic): Promise<void> {
+  try {
+    const b = await bridge();
+    if (kind === 'select') {
+      await b.send('VKWebAppTapticSelectionChanged', {});
+    } else if (kind === 'success' || kind === 'warning' || kind === 'error') {
+      await b.send('VKWebAppTapticNotificationOccurred', { type: kind });
+    } else {
+      await b.send('VKWebAppTapticImpactOccurred', { style: kind });
+    }
+  } catch {
+    // Outside VK / no taptic support: silent, like the Telegram haptic off-platform.
+  }
+}
+
+/**
+ * vkDisableSwipeBack turns off VK's horizontal swipe-back gesture (VKWebAppSetSwipeSettings with
+ * history:false) so it does not fight the app's own edge-swipe-back and on-board tile drag — the
+ * app owns navigation through its back chevron, as on Telegram (telegramDisableVerticalSwipes).
+ * Best-effort; a no-op outside VK or on a client without the method.
+ */
+export async function vkDisableSwipeBack(): Promise<void> {
+  try {
+    await (await bridge()).send('VKWebAppSetSwipeSettings', { history: false });
+  } catch {
+    // Outside VK / unsupported: VK's default gesture handling stays as-is.
+  }
+}