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/holdem.js

@@ -370,7 +370,12 @@
         return pot.sweep(s.plate, e.amount, { gap: 55 }).then(function () {
           potTotal.textContent = money(pot.amount);
           moveStack(e.seat, e.amount);
-          if (e.seat === me && e.amount > 0) FX.burst(s.plate, { count: 18 });
+          if (e.seat === me && e.amount > 0) {
+            FX.burst(s.plate, { count: 18 });
+            // A real haul makes it rain; a blind-steal doesn't, or poker would be
+            // raining money every thirty seconds. Twenty big blinds is a pot.
+            if (view && view.tier && e.amount >= 20 * view.tier.bb) FX.moneyRain({ count: 24 });
+          }
           return wait(260);
         });