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/app.css

@@ -171,6 +171,10 @@ html.app-shell body {
   /* No text selection anywhere by default; inputs opt back in below. */
   user-select: none;
   -webkit-user-select: none;
+  /* No tap-highlight flash on tappable elements. Android in-app WebViews (Telegram, VK) draw a
+     momentary selection-like box on a clickable node on tap — seen on the header title and the
+     back chevron; user-select does not govern it. Inherited, so this clears it app-wide. */
+  -webkit-tap-highlight-color: transparent;
 }
 
 input,