feat(home): Hero 动态粒子层（入场浮现后静止）

新增 hero-particle-field 组件作为 Hero L3 层：品牌红点缀、Canvas + rAF
仅在 ~600ms 入场窗运行后冻结为静态帧，遵守「无持续循环动画」动效铁律；
prefers-reduced-motion 退化为一次性静态帧。固定种子 PRNG 保证视觉快照可复现。
同步更新 home-content-v15 接入与单测、home 视觉基线。

Co-Authored-By: 阿睿 <workbuddy@tencent.com>

src/components/sections/hero-particle-field.test.tsx

@@ -0,0 +1,34 @@
+import { describe, it, expect, jest } from '@jest/globals';
+import { render, screen } from '@testing-library/react';
+import '@testing-library/jest-dom';
+import HeroParticleField from './hero-particle-field';
+
+jest.mock('@/hooks/use-reduced-motion', () => ({
+  useReducedMotion: jest.fn(() => false),
+}));
+
+describe('HeroParticleField - 动态粒子层（入场浮现后静止）', () => {
+  it('renders an aria-hidden, non-interactive canvas layer', () => {
+    render(<HeroParticleField />);
+    const canvas = screen.getByTestId('hero-particle-field');
+    expect(canvas.tagName).toBe('CANVAS');
+    expect(canvas).toHaveAttribute('aria-hidden', 'true');
+    expect(canvas.className).toContain('pointer-events-none');
+  });
+
+  it('does not throw under reduced motion (degrades to a single static frame)', () => {
+    const { useReducedMotion } = require('@/hooks/use-reduced-motion');
+    (useReducedMotion as jest.Mock).mockReturnValue(true);
+    expect(() => render(<HeroParticleField />)).not.toThrow();
+    // 静态降级下仍渲染 canvas（无 rAF 循环，仅一次绘制）
+    expect(screen.getByTestId('hero-particle-field').tagName).toBe('CANVAS');
+  });
+
+  it('bails safely when no 2d context is available (jsdom / SSR guard)', () => {
+    const ctxSpy = jest
+      .spyOn(HTMLCanvasElement.prototype, 'getContext')
+      .mockReturnValue(null as any);
+    expect(() => render(<HeroParticleField />)).not.toThrow();
+    ctxSpy.mockRestore();
+  });
+});