perf: 图片渐进加载,缩短首屏等待

- 流内单图改用缩略图(原图仅在灯箱按需加载),体积大幅减小
- BubbleImage 加 decoding=async + 加载完淡入(ark-img-fade),图片逐张出现
- 视频海报/文件预览/推荐卡/热门榜补 decoding=async、lazy
原图无缩略图时自动回退,无回归。

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/RecommendedCard.tsx

@@ -116,6 +116,7 @@ export function RecommendedCard({
             alt=""
             className="ark-img-fade h-full w-full object-cover transition duration-300 group-hover:scale-[1.02]"
             loading="lazy"
+            decoding="async"
             onLoad={(e) => e.currentTarget.classList.add("is-loaded")}
           />
         ) : (
@@ -223,6 +224,7 @@ export function ComingSoonRecommendedCard({
           alt=""
           className="h-full w-full object-cover opacity-75 grayscale-[15%]"
           loading="lazy"
+          decoding="async"
         />
         <span className="absolute left-3 top-3 rounded-md bg-ark-gold px-2.5 py-1 text-xs font-semibold text-black">
           即将到来