games: burial send-offs, money rain on wins, and honest stack targeting

Three front-end changes to the casino games:

- uno: a draw-card stack now names the seat it's actually pointed at
  ("+N on Beep") instead of always reading "+N on you". The bill reads
  v.turn, which the engine advances to the target when a draw card lands.

- uno: the No Mercy rule buries a seat with some ceremony now. bury()
  rolls one of four send-offs over the seat (or your hand, if it's you) —
  a rockslide that piles up, a tombstone, a coffin, or the Mega Man death
  burst — each with its own synth sound, and a static headstone under
  reduced motion. The "Buried on N" badge still rides alongside.

- all games: winning makes it rain. FX.moneyRain drops a curtain of bills
  and coins with a jackpot coin-cascade sound, gated by significance so it
  reads as a win and not as noise: hold'em keeps its light per-pot confetti
  and only rains on a real haul (>= 20bb), while the confetti stays the
  rare cherry (natural 21, full board clear, phrase solved outright).

internal/web/static/js/blackjack.js

@@ -265,13 +265,10 @@
     verdictEl.textContent = text;
     verdictEl.classList.remove("hidden");
 
-    // The one thing in this room that gets confetti. A natural is rare, it pays
-    // 3:2, and if everything celebrated then nothing would.
-    //
-    // The *sound* is not so precious: a win is a win and you should hear it. So
-    // the fanfare rides on the money, not on the confetti.
-    if (v.outcome === "blackjack") FX.burst(verdictEl, { count: 34 });
-    else if (v.net > 0) FX.sfx("win");
+    // Every win gets it to rain, because a win should feel like one. A natural is
+    // rarer and pays 3:2, so it keeps the confetti on top of the money as well.
+    if (v.outcome === "blackjack") { FX.burst(verdictEl, { count: 34 }); FX.moneyRain({ count: 30 }); }
+    else if (v.net > 0) FX.moneyRain();
     else if (v.net < 0) FX.sfx("lose");
     else FX.sfx("push");
   }