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/game/Game.svelte

@@ -24,7 +24,8 @@
   import { getCachedGame, setCachedGame, setCachedDraft, type CachedGame } from '../lib/gamecache';
   import { patchLobbyGame } from '../lib/lobbycache';
   import { applyGameOver, applyMoveDelta, applyOpponentJoined, type DeltaResult } from '../lib/gamedelta';
-  import { insideTelegram, telegramDialogsAvailable, telegramHaptic, telegramShowConfirm } from '../lib/telegram';
+  import { insideTelegram, telegramDialogsAvailable, telegramShowConfirm } from '../lib/telegram';
+  import { haptic } from '../lib/haptics';
   import {
     BLANK,
     newPlacement,
@@ -511,7 +512,7 @@
               if (drag && isCoarse() && !zoomed) {
                 focus = c;
                 zoomed = true;
-                telegramHaptic('light');
+                haptic('light');
               }
             }, 700)
           : null;
@@ -623,7 +624,7 @@
       return;
     }
     placement = place(placement, index, row, col);
-    telegramHaptic('select');
+    haptic('select');
     recompute();
     scheduleDraftSave();
   }
@@ -631,7 +632,7 @@
     if (!blankPrompt) return;
     placement = place(placement, blankPrompt.rackIndex, blankPrompt.row, blankPrompt.col, letter);
     blankPrompt = null;
-    telegramHaptic('select');
+    haptic('select');
     recompute();
     scheduleDraftSave();
   }
@@ -687,7 +688,7 @@
     busy = true;
     try {
       applyMoveResult(await gateway.submitPlay(id, sub.tiles, variant));
-      telegramHaptic('success');
+      haptic('success');
       zoomed = false;
     } catch (e) {
       handleError(e);
@@ -793,7 +794,7 @@
     shuffling = true;
     setTimeout(() => (shuffling = false), 600);
     // A short "shake": a few quick light taps rather than one.
-    for (let i = 0; i < 4; i++) setTimeout(() => telegramHaptic('light'), i * 55);
+    for (let i = 0; i < 4; i++) setTimeout(() => haptic('light'), i * 55);
     scheduleDraftSave();
   }
   function openExchange() {