fix(player): 合并外部贡献后的集成修复

- PlayBar 下载按钮补 isElectron 守卫，Web 端不再显示无效按钮（#708 评审意见）
- preloadNextSongs 恢复 800ms 短去抖，避免快速切歌时音源请求风暴（#712 评审意见）
- 清理合并后未使用的导入

src/renderer/components/player/PlayBar.vue

@@ -151,7 +151,7 @@
         </template>
         {{ t('player.playBar.reparse') }}
       </n-tooltip>
-      <n-tooltip v-if="playMusic?.id" trigger="hover" :z-index="9999999">
+      <n-tooltip v-if="playMusic?.id && isElectron" trigger="hover" :z-index="9999999">
         <template #trigger>
           <i
             class="iconfont ri-download-line"

src/renderer/hooks/usePlayerHooks.ts

@@ -6,8 +6,7 @@ import { getMusicLrc, getMusicUrl, getParsingMusicUrl } from '@/api/music';
 import { playbackRequestManager } from '@/services/playbackRequestManager';
 import { SongSourceConfigManager } from '@/services/SongSourceConfigManager';
 import type { ILyric, ILyricText, IWordData, SongResult } from '@/types/music';
-import { getImgUrl, isElectron } from '@/utils';
-import { getImageLinearBackground } from '@/utils/linearColor';
+import { isElectron } from '@/utils';
 import { parseLyrics as parseYrcLyrics } from '@/utils/yrcParser';
 
 const { message } = createDiscreteApi(['message']);

src/renderer/store/modules/playlist.ts

@@ -107,9 +107,19 @@ export const usePlaylistStore = defineStore(
     };
 
     /**
-     * 智能预加载下一首歌曲（立即执行，不等待）
+     * 智能预加载下一首歌曲
+     * 短去抖：快速连续切歌时只保留最后一次，避免对音源 API 的请求风暴
      */
+    let preloadDebounceTimer: ReturnType<typeof setTimeout> | null = null;
     const preloadNextSongs = (currentIndex: number) => {
+      if (preloadDebounceTimer) clearTimeout(preloadDebounceTimer);
+      preloadDebounceTimer = setTimeout(() => {
+        preloadDebounceTimer = null;
+        doPreloadNextSongs(currentIndex);
+      }, 800);
+    };
+
+    const doPreloadNextSongs = (currentIndex: number) => {
       if (playList.value.length <= 1) return;
 
       let nextIndex: number;