refactor: 移除下载部分组件及样式，优化项目结构

- 删除DownloadSection组件及其相关CSS，简化代码结构
- 在历史页面中添加生成中任务的进度计算和显示功能
- 更新历史页面样式，增强用户体验和视觉效果
- 添加缩略图毛玻璃蒙版和进度指示器，提升信息传达的清晰度

src/pages/history/index.css

@@ -274,3 +274,92 @@
   font-weight: 500;
   letter-spacing: 0.5px;
 }
+
+/* 缩略图毛玻璃蒙版 */
+.thumbnail-overlay {
+  position: absolute;
+  inset: 0;
+  border-radius: 12px;
+  overflow: hidden;
+  z-index: 10;
+  pointer-events: none;
+}
+
+.thumbnail-glassmorphism {
+  position: absolute;
+  inset: 0;
+  background: linear-gradient(135deg, rgb(255 255 255 / 80%) 0%, rgb(255 255 255 / 70%) 50%, rgb(255 255 255 / 85%) 100%);
+  backdrop-filter: blur(6px);
+}
+
+.thumbnail-progress {
+  position: relative;
+  z-index: 2;
+  height: 100%;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.thumbnail-progress-circle {
+  width: 100px;
+  height: 100px;
+  border-radius: 50%;
+  position: relative;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: transparent;
+  animation: pulse 2s ease-in-out infinite;
+}
+
+.thumbnail-progress-fill {
+  position: absolute;
+  inset: 0;
+  border-radius: 50%;
+  background: conic-gradient(#ff9500 0deg, transparent 0deg);
+  transition: all 0.3s ease;
+  mask: radial-gradient(circle at center, transparent 42px, black 45px);
+}
+
+.thumbnail-progress-inner {
+  width: 90px;
+  height: 90px;
+  border-radius: 50%;
+  background: transparent;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  position: relative;
+  z-index: 2;
+}
+
+.thumbnail-progress-text {
+  font-size: 28px;
+  color: #ff9500;
+  text-shadow: 0 1px 2px rgb(0 0 0 / 20%);
+}
+
+/* 动画效果 */
+@keyframes pulse {
+  0%,
+  100% {
+    transform: scale(1);
+    opacity: 1;
+  }
+
+  50% {
+    transform: scale(1.05);
+    opacity: 0.8;
+  }
+}
+
+@keyframes shimmer {
+  0% {
+    background-position: -200px 0;
+  }
+
+  100% {
+    background-position: calc(200px + 100%) 0;
+  }
+}