Story phase 4: help when stuck, the arcade opens with the story

- From the third attempt at a checkpoint, the death screen offers TRY
  AGAIN · WITH HELP, at most two tiers, said openly. In the cup the help
  is fresher legs and a longer swing; in gore, one more heart and a
  slower director and horde. Every checkpoint passed resets the offer.
- The arcade shows only what the story has opened. Training and Classic
  open after act I, the Climb after II, Splatter Gore after III, and
  hosting a friend after IV (joining stays free). Locked doors are shown
  greyed with the act that opens them.
- The non-story endings point at the story instead of the cup.
- Store switches for the free tier (act I's card points at the full
  game) and a premium arcade, both off.
- The prologue's HUD no longer overlaps the kill pips.

PROJECT.md logs phases 1-4. One new test. v382, staging only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/zombies.js

@@ -3,7 +3,7 @@
 // your baseline — one crossing it is a point for THEM.
 // (zombies <-> gameplay is a runtime-only import cycle, same pattern as input.)
 
-import { TUNE, UI, COURT, CONTACT, BOSS_ART, bossArt, WEAPONS, BARREL_WEAPONS, TIN_LEAGUE, woundStage, zombieH, EATEN_BURST, EATEN_SUMMARY, EATEN_FEED_R, storyPool } from './config.js';
+import { TUNE, UI, COURT, CONTACT, BOSS_ART, bossArt, WEAPONS, BARREL_WEAPONS, TIN_LEAGUE, woundStage, zombieH, EATEN_BURST, EATEN_SUMMARY, EATEN_FEED_R, storyPool, STORY_HELP } from './config.js';
 import { G, P, O, ball, score, sendBoy, setupPoint } from './state.js';
 import { splat, moan, pock, thud, zap, voice, boom, swish, shriek, aww, sfx , whoosh, flame, squeak, crackle, whump, gunshot, stomp, growl } from './audio.js';
 import { haptic } from './haptics.js';
@@ -1070,7 +1070,8 @@ export function updateZombies(dt) {
       if (spawnT <= 0 && zombies.length < cap) {
         spawnZombie((Math.random() * 2 - 1) * 4.8, -1.5 - Math.random(), pickVariant());
         spawnT = G.testMode ? TUNE.testSpawnEvery
-          : Math.max(TUNE.zSpawnMin, TUNE.zSpawnEvery / (1 + G.runGames * TUNE.zSpawnAccel));
+          : Math.max(TUNE.zSpawnMin, TUNE.zSpawnEvery / (1 + G.runGames * TUNE.zSpawnAccel))
+            * (G.story && G.story.help ? 1 + STORY_HELP.slow * G.story.help : 1);   // THE STORY's help offer
       }
     }
   }