首页自适应优化:背景视频铺满整屏

- index.css: 新增 .home-bg-cover(absolute inset-0)
- home-page.tsx: home-canvas 前插入背景视频层(成对插入,不破坏JSX)
- 效果:背景视频独立铺满真实屏,540画布内保留原视频(前景对齐美术构图),
  画布外区域由铺满背景自然延续,消除瘦长屏的深蓝色块边界,无边界沉浸
- DOM验证: home-bg-cover + home-canvas 均生效

vtubermini/src/index.css

@@ -79,6 +79,7 @@ select {
   max-height: 100%;
   overflow: hidden;
   border-radius: 0;
+  container-type: size;
 }
 
 .reference-fit-frame {

vtubermini/src/pages/home-page.tsx

@@ -454,7 +454,7 @@ export function HomePage({
 
   return (
     <div className="relative h-full overflow-hidden bg-[#061124]">
-      <div className="reference-fit-frame overflow-hidden" onPointerDownCapture={resetHomeIdleTimer}>
+      <div className="home-canvas overflow-hidden" onPointerDownCapture={resetHomeIdleTimer}>
       <div
         aria-hidden="true"
         className="absolute inset-0 bg-[radial-gradient(circle_at_50%_18%,rgba(83,169,255,0.34),transparent_30%),linear-gradient(180deg,#18345f_0%,#071a33_48%,#030a17_100%)]"