refactor(chronos): 粒子渲染 WebGL 单网格→Canvas 2D 伪 3D 重构

- 移除 ChronosCreature/ChronosParticleField（WebGL 双网格实现）
- 新增 ChronosParticleField2D：Canvas 2D 伪 3D 粒子场（统一性能档位）
- 新增 particleDistribution 确定性分布算法与单元测试
- particleMorphs 形态插值适配 2D 渲染；ChronosSphere 保留 WebGL 高配路径

Author: Aparencia

client/src/features/pomodoro/components/chronos/ChronosCanvas.tsx

@@ -81,7 +81,7 @@ export const ChronosCanvas = memo(function ChronosCanvas({
 
   // ── 时间显示隐藏化：父组件传入 showTime（阶段开始 5s），hover 粒子团时显示 ──
   const [hovering, setHovering] = useState(false);
-  const timeVisible = showTime || hovering;
+  const timeVisible = chronosState !== 'asleep' && (showTime || hovering);
 
   // 容器层统一手势
   const pointerDownRef = useRef(0);