Add chapter bosses and a second damage channel; demote the racket zombie

Steps 4 and 5 of the late-game depth plan.

The ranged channel. A rogue ball machine gets wheeled onto the far court every
four games: it never walks, never crosses your baseline and never scores, so
it is a standing threat you choose when to deal with — the target-priority
decision the game was missing. Its shot is a real arc solved like a serve, not
a flat bolt, so it reads coming in and the swing window has something to meet.
Three outcomes: a swing inside the volley window returns it as your own ball
flying up-court (an extras clone, so "a parry is a weapon" cost nothing to
build), the panic swish bats it away, and letting it reach you costs blood.
The swish path is load-bearing, not politeness: in pretoss the player is
rooted and cannot swing at all.

Contact still kills outright — that stays a separate channel, and killPlayer()
is now the single death path for both causes so the run summary and the best-run
write cannot drift. Health is drawn on the man: procedural spatter at fixed
anchors, a live trickle, and a red wash from the screen edges. No bar. Healing
is winning a duel, which finally gives the duel a reason to be wanted.

Chapter bosses every ten games, with their own sheet — a colossal zombie
groundskeeper hauling a ball hopper, coming apart through arm-off, ribs-out and
headless-still-throwing. Chapter 1 is 10 hp and 2.7 m, chapter 4 is 34 hp and
3.67 m. It outranks the set and duel beats at a clear, because a boss walking
into a standing wave is unreadable. And it fixes the economy: a chapter-4 boss
costs 12 bombs or 100 rounds or 34 side balls against a per-type cap of 9, so
no single weapon can take one and a banked mixed arsenal is mandatory.

The racket zombie is demoted to an occasional opponent, as asked — appearing
every won game is exactly why he read as the boss.

Five silent bugs found on the way, all in HANDOFF: a blast deleted a 34 hp boss
outright (isBoss() exists to stop that class recurring), the machine's hp did
nothing because it fell through to the one-shot fallback, the boss both scored
and fired its card, the machine gated the hand-clear, and a boss died with a
shambler-sized gore burst.

Tennis untouched: 30 tapped points still 50 hits / 0 whiffs. 45-game soak clean
with all four chapters firing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

main.js

@@ -5,10 +5,10 @@
 
 import { TUNE, COURT, UMP_H, UMP_X, EATEN_RESTART } from './config.js';
 import { P, O, ball, score, G, setupPoint } from './state.js';
-import { update, keyPressed, solveShot, inServeBox, inCourt, forceZombies, splatPoint, deliverTin, selectWeapon, showModal, dismissModal, startDuel, resolveInterlude, flickTarget } from './gameplay.js';
+import { update, keyPressed, solveShot, inServeBox, inCourt, forceZombies, splatPoint, deliverTin, selectWeapon, showModal, dismissModal, startDuel, resolveInterlude, flickTarget, startBossFight, endBossFight } from './gameplay.js';
 import { fitViewport, render, proj, RES } from './render.js';
 import { voice, ambient } from './audio.js';
-import { zombies, spawnZombie, piles, gore, parts, pellets, extras, explode } from './zombies.js';
+import { zombies, spawnZombie, spawnRacketZombie, spawnMachine, spawnChapterBoss, piles, gore, parts, pellets, extras, shots, explode, hurtPlayer, killPlayer } from './zombies.js';
 import { cv } from './dom.js';
 import './input.js';
 
@@ -58,6 +58,6 @@ 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, extras, explode, splatPoint, solveShot, inServeBox, inCourt, proj, setupPoint, forceZombies, deliverTin, selectWeapon, showModal, dismissModal, startDuel, resolveInterlude, flickTarget,
+window.T = { TUNE, ball, P, O, score, G, zombies, spawnZombie, spawnRacketZombie, spawnMachine, spawnChapterBoss, piles, gore, parts, pellets, extras, shots, explode, hurtPlayer, killPlayer, splatPoint, solveShot, inServeBox, inCourt, proj, setupPoint, forceZombies, deliverTin, selectWeapon, showModal, dismissModal, startDuel, resolveInterlude, flickTarget, startBossFight, endBossFight,
   step: dt => update(dt), render, press: keyPressed,
   get phase() { return G.phase; }, set phase(v) { G.phase = v; } };