Phase 0: drivable car with persistent wear

Vite + TypeScript + three.js + Rapier raycast vehicle, fixed 60 Hz step.

Flat plate, seeded obstacle scatter, chase camera, debug HUD. Car condition
(engine/tires/chassis) degrades permanently and is derived into handling
numbers, so decline is felt through the wheel rather than read off a meter.

src/sim/ is kept free of three.js and Rapier imports — the later heat, region
and front-line systems all live there, and staying engine-free is what makes
them unit-testable without a browser.

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

src/ui/hud.ts

@@ -0,0 +1,31 @@
+import type { CarCondition } from '../sim/car';
+
+const BAR_WIDTH = 12;
+
+function bar(value: number): string {
+  const filled = Math.round(value * BAR_WIDTH);
+  return '█'.repeat(filled) + '·'.repeat(BAR_WIDTH - filled);
+}
+
+export function createHud(seed: number) {
+  const el = document.getElementById('hud')!;
+  let last = 0;
+
+  return {
+    update(speedMs: number, condition: CarCondition, now: number) {
+      // The HUD is debug scaffolding, not the real interface — 10 Hz is plenty.
+      if (now - last < 0.1) return;
+      last = now;
+      el.textContent = [
+        `${Math.abs(speedMs * 3.6).toFixed(0).padStart(3)} km/h`,
+        '',
+        `engine  ${bar(condition.engine)} ${(condition.engine * 100).toFixed(0)}%`,
+        `tires   ${bar(condition.tires)} ${(condition.tires * 100).toFixed(0)}%`,
+        `chassis ${bar(condition.chassis)} ${(condition.chassis * 100).toFixed(0)}%`,
+        '',
+        `seed ${seed}`,
+        'WASD drive · space handbrake · R respawn',
+      ].join('\n');
+    },
+  };
+}