perf: 优化图片消息后台加载与解密缓存

- 缩略图优先展示并在后台准备原图
- 增加图片请求去重与受控并发队列
- 缓存图片路径、账号目录和解密结果

src/preload/index.ts

@@ -61,7 +61,7 @@ const api = {
     imageMd5?: string,
     imageDatNameOrThumb?: string | boolean,
     sessionId?: string,
-    options?: { force?: boolean }
+    options?: { force?: boolean; preferThumbnail?: boolean }
   ) => ipcRenderer.invoke('db:getImage', imageMd5, imageDatNameOrThumb, sessionId, options),
   getVideo: (hashes: string[]) => ipcRenderer.invoke('db:getVideo', hashes),
   getSticker: (cdnUrl?: string, md5?: string) => ipcRenderer.invoke('db:getSticker', cdnUrl, md5),