feat: 曲库索引 —— 曲库里已有的同名歌曲在列表中标记「曲库」

不是通过声匣下载的文件（其他工具 / 手动放入）以前一律显示未下载。
现在启动时扫描音乐目录，按「歌名 + 歌手文件夹 / 专辑文件夹」匹配，
下载完成增量更新，每 30 分钟或删除 / 补全标签后重建；设置页可手动重建。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/components/TrackList.vue

@@ -35,7 +35,8 @@ watch(
 );
 
 const allSelected = computed(() => props.tracks.length > 0 && selected.value.size === props.tracks.length);
-const pendingCount = computed(() => props.tracks.filter((t) => !isDownloaded(t)).length);
+const owned = (t: TrackSummary) => isDownloaded(t) || !!t.inLibrary;
+const pendingCount = computed(() => props.tracks.filter((t) => !owned(t)).length);
 
 function toggleRow(index: number, e: MouseEvent) {
   const next = new Set(selected.value);
@@ -56,7 +57,7 @@ function toggleAll() {
 }
 
 function selectPending() {
-  selected.value = new Set(props.tracks.filter((t) => !isDownloaded(t)).map((t) => t.id));
+  selected.value = new Set(props.tracks.filter((t) => !owned(t)).map((t) => t.id));
 }
 
 async function downloadSelected() {
@@ -69,7 +70,14 @@ function downloadAll() {
   download(props.tracks, quality.value, props.group);
 }
 
-function rowState(t: TrackSummary) {
+interface RowState {
+  kind: string;
+  text: string;
+  pct: number;
+  title?: string;
+}
+
+function rowState(t: TrackSummary): RowState | null {
   const task = activeByTrack.value.get(trackKey(t.source, t.id));
   if (task) {
     if (task.status === 'running') {
@@ -80,6 +88,7 @@ function rowState(t: TrackSummary) {
     return { kind: task.status, text: task.status === 'paused' ? '已暂停' : '排队中', pct: 0 };
   }
   if (isDownloaded(t)) return { kind: 'done', text: '已下载', pct: 1 };
+  if (t.inLibrary) return { kind: 'library', text: '曲库中有', pct: 1, title: `曲库中有同名歌曲：${t.inLibrary}` };
   return null;
 }
 
@@ -158,9 +167,9 @@ const best = (t: TrackSummary) => bestQuality(t.qualities);
         </span>
         <span class="state">
           <template v-if="rowState(t)">
-            <span class="st" :class="rowState(t)!.kind">
-              <Icon v-if="rowState(t)!.kind === 'done'" name="check" :size="14" />
-              {{ rowState(t)!.kind === 'done' ? '' : rowState(t)!.text }}
+            <span class="st" :class="rowState(t)!.kind" :title="rowState(t)!.title ?? rowState(t)!.text">
+              <Icon v-if="rowState(t)!.kind === 'done' || rowState(t)!.kind === 'library'" name="check" :size="14" />
+              {{ rowState(t)!.kind === 'done' ? '' : rowState(t)!.kind === 'library' ? '曲库' : rowState(t)!.text }}
             </span>
             <span v-if="rowState(t)!.kind === 'running'" class="bar"><i :style="{ width: `${rowState(t)!.pct * 100}%` }" /></span>
           </template>
@@ -392,6 +401,11 @@ const best = (t: TrackSummary) => bestQuality(t.qualities);
   font-family: var(--font-mono);
 }
 
+.st.library {
+  color: var(--ink-3);
+  cursor: help;
+}
+
 .st.done {
   color: var(--ok);
 }