Game/Telegram review polish: USSR flag, touch drag ghost, TG fullscreen header

Backlog item 2 of ~4 (owner review pass):
- USSR flag emblem redrawn (canonical hammer & sickle, scaled down 1.5x
  below the star).
- Touch drag-and-drop: enlarge the drag ghost 1.5x on touch only (the finger
  hides the tile); suppress the iOS tap-highlight that lingered on a rack tile
  sliding into a dragged tile's slot.
- Telegram fullscreen: its native nav no longer hides our header -- the header
  drops below the content-safe-area top inset and the menu (hamburger) lifts
  into the nav band, centred (--tg-content-top from the SDK inset + a
  tg-fullscreen class; new telegram.ts helper + app wiring).

Tests: UI check/test:unit/build + full e2e (60) green. The iOS tap-highlight
fix and the TG-fullscreen layout want on-device verification on the deploy.

ui/src/game/Game.svelte

@@ -60,7 +60,7 @@
   let checkResult = $state<{ word: string; legal: boolean } | null>(null);
   let resignOpen = $state(false);
   let messages = $state<ChatMessage[]>([]);
-  let drag = $state<{ letter: string; blank: boolean; x: number; y: number } | null>(null);
+  let drag = $state<{ letter: string; blank: boolean; x: number; y: number; touch: boolean } | null>(null);
 
   const checkedWords = new Map<string, boolean>();
   let cooling = $state(false);
@@ -315,7 +315,7 @@
       const src = downInfo.src;
       const letter =
         src.from === 'rack' ? placement.rack[src.index] : pendingMap.get(`${src.row},${src.col}`)?.letter ?? '';
-      drag = { letter, blank: letter === BLANK, x: e.clientX, y: e.clientY };
+      drag = { letter, blank: letter === BLANK, x: e.clientX, y: e.clientY, touch: e.pointerType === 'touch' };
       // A rack tile is lifted out of the rack while dragged (the ghost stands in for it).
       reorderDragId = src.from === 'rack' ? rackIds[src.index] ?? null : null;
       // No zoom on drag start: the player may still change their mind. Holding the tile
@@ -814,7 +814,7 @@
 </Screen>
 
 {#if drag}
-  <div class="ghost" style="left:{drag.x}px; top:{drag.y}px">
+  <div class="ghost" class:touch={drag.touch} style="left:{drag.x}px; top:{drag.y}px">
     <span>{drag.blank ? '' : drag.letter}</span>
   </div>
 {/if}
@@ -1092,6 +1092,10 @@
     pointer-events: none;
     z-index: 60;
   }
+  /* On touch the finger covers the tile, so enlarge the drag ghost ~1.5x (Stage 17). */
+  .ghost.touch {
+    transform: translate(-50%, -50%) scale(1.5);
+  }
   .alpha {
     display: grid;
     grid-template-columns: repeat(6, 1fr);