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/app.css

@@ -41,6 +41,9 @@
   --radius-sm: 6px;
   --gap: 8px;
   --pad: 12px;
+  /* Height Telegram's native nav overlays at the top in fullscreen; set from the SDK's
+     content-safe-area inset (Stage 17), 0 elsewhere. */
+  --tg-content-top: 0px;
   --font: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial,
     "Noto Sans", "Liberation Sans", sans-serif;
   --shadow: 0 1px 2px rgba(0, 0, 0, 0.08), 0 6px 16px rgba(0, 0, 0, 0.06);