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/app.svelte.ts

@@ -23,7 +23,6 @@ import {
   telegramSafeAreaInset,
   telegramDisableVerticalSwipes,
   telegramShowSettingsButton,
-  telegramHaptic,
   telegramLaunch,
   type TelegramLaunch,
   telegramOnEvent,
@@ -32,7 +31,8 @@ import {
   telegramCloudGet,
   telegramCloudSet,
 } from './telegram';
-import { onVKPath, insideVK, vkInit, vkLaunchParams, vkUserName, vkStartParam, vkOnScheme, vkOnInsets } from './vk';
+import { onVKPath, insideVK, vkInit, vkDisableSwipeBack, vkLaunchParams, vkUserName, vkStartParam, vkOnScheme, vkOnInsets } from './vk';
+import { haptic } from './haptics';
 import { CLOUD_PREFS_KEY, decodeClientPrefs, encodeClientPrefs } from './cloudprefs';
 import { parseStartParam } from './deeplink';
 import {
@@ -281,7 +281,7 @@ export function handleError(err: unknown): void {
     return;
   }
   if (isConnectionCode(code) || !connection.online) return;
-  telegramHaptic('error');
+  haptic('error');
   showToast(t(code ? errorKey(code) : 'error.generic'), 'error');
 }
 
@@ -705,6 +705,9 @@ export async function bootstrap(): Promise<void> {
       root.style.setProperty('--tg-safe-right', `max(env(safe-area-inset-right, 0px), ${i.right}px)`);
     });
     await vkInit();
+    // The app owns navigation (its own back chevron), so silence VK's horizontal swipe-back to keep
+    // it off our edge-swipe-back and on-board tile drag — parity with telegramDisableVerticalSwipes.
+    void vkDisableSwipeBack();
     await bootVK();
     app.ready = true;
     return;