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/messageStream/bubbles/FileDocBubble.tsx

@@ -45,6 +45,7 @@ function AttachmentRow({ postId, att }: { postId: string; att: Attachment }) {
           src={previewUrl}
           alt=""
           loading="lazy"
+          decoding="async"
           onError={() => setPreviewFailed(true)}
           className="h-16 w-16 shrink-0 rounded-lg object-cover"
         />

src/components/messageStream/bubbles/SingleImageFrame.tsx

@@ -20,6 +20,11 @@ export function SingleImageFrame({
   return (
     <AdaptiveImageFrame
       attachment={attachment}
+      // Show the lightweight thumbnail in-stream for fast, progressive loading;
+      // the full image is loaded on tap in the lightbox. Falls back to the full
+      // asset if no thumbnail exists.
+      src={attachment.thumbnailUrl ?? attachment.thumbUrl ?? attachment.url}
+      fallbackSrc={[attachment.thumbUrl, attachment.url]}
       onOpen={() => openLightbox([attachment], 0, text, postId)}
       ariaLabel="View image"
     >

src/components/messageStream/bubbles/VideoBubble.tsx

@@ -1,4 +1,4 @@
-import { LoaderCircle, Maximize2, Play, X } from "lucide-react";
+import { LoaderCircle, Play, X } from "lucide-react";
 import { DownloadCloudIcon } from "../../icons/DownloadCloudIcon";
 import { useEffect, useRef, useState } from "react";
 import { createPortal } from "react-dom";
@@ -79,10 +79,12 @@ function VideoAttachmentCard({
             src={attachment.url}
             poster={attachment.posterUrl}
             controls
+            controlsList="nodownload noplaybackrate noremoteplayback"
+            disablePictureInPicture
             playsInline
             autoPlay
             onClick={(e) => e.stopPropagation()}
-            className="absolute inset-0 h-full w-full"
+            className="ark-message-video absolute inset-0 h-full w-full"
           />
           <AttachmentDownloadPill
             postId={postId}
@@ -90,18 +92,6 @@ function VideoAttachmentCard({
             leadingLabel={duration}
             className="absolute left-2 top-2 z-20"
           />
-          <button
-            type="button"
-            onClick={(e) => {
-              e.stopPropagation();
-              const v = videoRef.current;
-              openVideo(attachment, v?.currentTime ?? 0);
-            }}
-            className="absolute right-2 top-2 z-20 flex h-9 w-9 items-center justify-center rounded-full bg-black/60 text-white shadow-lg ring-1 ring-white/25 transition hover:bg-black/80"
-            aria-label="Fullscreen"
-          >
-            <Maximize2 className="h-4 w-4" strokeWidth={2.2} />
-          </button>
         </>
       ) : (
         <>
@@ -109,6 +99,8 @@ function VideoAttachmentCard({
             <img
               src={posterUrl}
               alt=""
+              loading="lazy"
+              decoding="async"
               className={`absolute inset-0 h-full w-full object-cover ${
                 overlayCount ? "blur-sm scale-105" : ""
               }`}
@@ -284,6 +276,8 @@ function VideoListDialog({
                       <img
                         src={thumb}
                         alt=""
+                        loading="lazy"
+                        decoding="async"
                         className="h-full w-full object-cover"
                       />
                     ) : (