Splatter feel pass: melee, homing, multi-ball, clearer MG mode

From Oliver's feedback round:

- Racket melee: any swish (tap) in splatter cleaves shamblers within
  TUNE.meleeRange (1.7m) — a close-range survival tool. Works during a
  horde too (tap = swish only, still no serve). The racket-zombie boss
  (Phase 6, not built) is immune by design.
- Zombies home in on you: on YOUR half (z > netZ) they now drift toward
  P.x instead of walking a straight lane; far half stays an aimless
  shamble.
- Multi-ball / rapid fire: splatter is now a shooter — every tap/flick
  fires immediately (dropped the toss ritual there), and serving while a
  ball still flies stashes the old one into a new extraBalls array so it
  keeps arcing and killing (cap 6). Refactored the kill into a shared
  killZombie() with no ball coupling, used by ball hits, pellets, melee,
  and extra balls.
- Machine-gun mode clarity: confirmed free-walk (drag/arrows move you,
  auto-assist off) and tap-doesn't-serve during a horde; added a
  code-drawn "rambo" racket held forward with a muzzle flash over the
  player, and a splatter-specific serve prompt.

REVIEW on your phone — two opinionated calls, both easy to revert:
1. Dropped the toss in splatter (tap = instant quick-serve, pow 0.62).
   Rapid fire, but no apex-timing quality/pierce. Want the toss back as
   an option?
2. MG posture is a code-drawn forward racket, not a real body sprite —
   good enough, or worth a proper p_mg sprite later?
Also: each rapid serve still auto-consumes a stocked bomb, so bombs
deplete fast now — flag if that feels wrong.

Verified via window.T: melee kills a 1.0m zombie and spares a 4.5m one;
a near-half zombie drifts x 3→1.9 toward you; firing twice leaves 1
stashed ball + a fresh serve (barrage screenshot); extra balls kill and
pierce; free-walk during a horde (x 0→2.7); horde-tap melees without
serving; tennis toss-serve and Phase-4 bomb consume still work; no
console errors.

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

main.js

@@ -8,7 +8,7 @@ import { P, O, ball, score, G, setupPoint } from './state.js';
 import { update, keyPressed, solveShot, inServeBox, inCourt, forceZombies } from './gameplay.js';
 import { fitViewport, render, proj } from './render.js';
 import { voice } from './audio.js';
-import { zombies, spawnZombie, piles, gore, parts, pellets } from './zombies.js';
+import { zombies, spawnZombie, piles, gore, parts, pellets, extraBalls } from './zombies.js';
 import { cv } from './dom.js';
 import './input.js';
 
@@ -54,6 +54,6 @@ cv.addEventListener('pointerdown', e => {
 requestAnimationFrame(frame);
 
 // exposed for in-browser sanity checks and simulated playtests
-window.T = { TUNE, ball, P, O, score, G, zombies, spawnZombie, piles, gore, parts, pellets, solveShot, inServeBox, inCourt, proj, setupPoint, forceZombies,
+window.T = { TUNE, ball, P, O, score, G, zombies, spawnZombie, piles, gore, parts, pellets, extraBalls, solveShot, inServeBox, inCourt, proj, setupPoint, forceZombies,
   step: dt => update(dt), render, press: keyPressed,
   get phase() { return G.phase; }, set phase(v) { G.phase = v; } };