Zombie mode: kills-per-point knob so a game isn't 4 pot-shots

1 kill = 1 point made a tennis game trivially short (4 kills). Gate
player scoring behind TUNE.killsPerPoint (default 3) — K kills bank one
point, the rest just splatter. Opponent breaches stay 1-for-1, so the
asymmetry is where the pressure comes from. Live-tunable in the T panel;
set to 1 to restore the old behavior.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

state.js

@@ -44,6 +44,7 @@ export const G = {
   interlude: false,   // sudden-death duel vs the racket zombie: falsy, or {introT} while announcing
   duelLerp: 0,        // 0..1 — how far the court has returned to tennis colors for the duel
   horde: null,        // active horde wave {t, spawnT, mgT} — machine-gun racket, no serving
+  killCount: 0,       // splatter: kills banked toward the next point (see TUNE.killsPerPoint)
   runGames: 0,        // games finished this run (either side) — the difficulty director
   sets: [0, 0],       // splatter sets won [you, them]; 6 games = a set = a horde
   changeover: false,  // the odd-game breather: no spawns, no serving, the boys mop