chore(ui): change hints symbol for backward unicode compatibility

docs/UI_DESIGN.md

@@ -53,7 +53,7 @@ dismisses as soon as the lobby is ready. The pure layout and timing live in `lib
 
 A one-time **coachmark overlay** introduces the interface to a new player. Like the splash it is an
 **App-level overlay**; it runs two independent series chosen by the route — **lobby** (⚙️ settings →
-✏️ stats → 🎲 new game) and **game** (scoreboard header → 🔄 pass/exchange → 🛟 hints → 🔀 shuffle →
+✏️ stats → 🎲 new game) and **game** (scoreboard header → 🔄 pass/exchange → ✨ hints → 🔀 shuffle →
 rack). It draws **one bubble at a time** over a light scrim (`rgba(0,0,0,0.32)`); the whole layer
 captures pointer events, so a **tap anywhere advances** and the UI underneath stays inert. After the
 last hint the series is recorded done (`session.ts` `onboarding` key) and the overlay removes itself;
@@ -284,7 +284,7 @@ e2e and the screenshots.
   opens a dialog — pick tiles to **Exchange N**, or pick
   none to **Pass without exchanging**; pass is always available on your turn, exchange only
   while the bag still holds a full rack, below which the tiles disable and only the pass
-  remains), 🛟 Hint (with a remaining-count badge, disabled at zero); 🔀 Shuffle (no label,
+  remains), ✨ Hint (with a remaining-count badge, disabled at zero); 🔀 Shuffle (no label,
   no confirm), which
   **animates** — tiles hop along a low parabola to their new slots (duration scaled by the
   distance, the longest ≤ 0.3 s; off under reduce-motion) with a short haptic shake. A **thin strip