Phase 12: the weapon ladder — every tin opens something nastier

Deliveries cycle BOMB -> TRIPLE -> FIRE -> GUN (G.deliveries indexes the
ladder); one tin at a time, a fresh delivery replaces unspent stock. All
weapons stay one-thumb: the serve auto-consumes, zero new inputs.

- Triple serve (x3): one real serve fans two ballistic clones +-6deg (extras[]
  in zombies.js — NOT the reverted rapid-fire: each fan costs a proper serve).
  Side balls respect variant rules (wound brutes, clank off chairs, pass the boss)
- Flame ball (x3): kills on ANY contact regardless of pow, chair ignored,
  full pierce (splatter pace tax undone), ember trail, white-hot render
- Machine gun (8s): horde auto-fire as a pickup — no serving, drag steers,
  no assist, spawner keeps running, ammo bar drains on the HUD, then the
  serve loop resumes
- HUD pips per type (black/yellow/orange) at the bomb slot; flash names the
  tin ('NEW BALLS: FIRE')

Verified: ladder cycles across 5 deliveries; triple spawns 2 extras and the
fan kills flanked targets; pow-0.1 flame ball clears shambler+shield+brute in
one pass with TRIPLE KILL chaining; GUN tin arms at changeover, blocks taps,
streams pellets (kill in 5 frames), expires back to pretoss; tennis 11/12;
no weapon-flag leaks into tennis; no console errors.

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

config.js

@@ -35,6 +35,7 @@ export const TUNE = {
   hordeLen: 12,     // s a horde wave lasts
   hordeRate: 2.5,   // zombies spawned per second during a horde
   mgRate: 6,        // machine-gun pellets fired per second during a horde
+  mgPickupLen: 8,   // s the machine-gun tin (4th delivery) auto-fires outside hordes
   runnerSpeed: 3.2, // runner ('f') speed multiplier over the shamble
   bruteHp: 2,       // splat-quality hits (or pellets) a brute ('g') soaks before it dies
   shieldDown: 1.5,  // s a shield zombie's ('s') chair stays dropped after a block — the kill window