feat: collapsible playlist groups + per-playlist download in Library

Library channel cards now collapse their playlist groups by default
(single-group sources auto-expand), and each group header has a
Download button that queues just that playlist's pending videos.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/renderer/src/components/LibraryView.tsx

@@ -152,7 +152,10 @@ const useStyles = makeStyles({
     alignItems: 'center',
     gap: '8px',
     padding: '6px 4px',
-    color: tokens.colorNeutralForeground2
+    color: tokens.colorNeutralForeground2,
+    cursor: 'pointer',
+    ...shorthands.borderRadius(tokens.borderRadiusMedium),
+    ':hover': { backgroundColor: tokens.colorNeutralBackground1Hover }
   },
   groupTitle: { fontWeight: tokens.fontWeightSemibold, flexGrow: 1, minWidth: 0 },
   row: {
@@ -250,6 +253,9 @@ export function LibraryView(): React.JSX.Element {
   const [selected, setSelected] = useState<Set<string>>(new Set())
   const [batchNote, setBatchNote] = useState<string | null>(null)
   const [syncNote, setSyncNote] = useState<string | null>(null)
+  // Which playlist groups are expanded. Empty = all collapsed (the default), so
+  // an expanded source shows just its group headers until one is opened.
+  const [expandedGroups, setExpandedGroups] = useState<Set<string>>(new Set())
   const [scheduled, setScheduled] = useState(false)
 
   const watchedCount = sources.filter((s) => s.watched).length
@@ -278,6 +284,7 @@ export function LibraryView(): React.JSX.Element {
   useEffect(() => {
     setSelected(new Set())
     setBatchNote(null)
+    setExpandedGroups(new Set())
   }, [selectedSourceId])
 
   // Live per-URL queue status so a video row reflects its real download state.
@@ -289,15 +296,21 @@ export function LibraryView(): React.JSX.Element {
 
   const items = selectedSourceId ? (itemsBySource[selectedSourceId] ?? []) : []
   const groups = useMemo(() => groupByPlaylist(items), [items])
+  // A group is shown when toggled open, or auto-expanded when it's the only group
+  // (a single "Uploads" channel shouldn't need a second click to reach its videos).
+  const isGroupOpen = (title: string): boolean =>
+    groups.length === 1 || expandedGroups.has(title)
   // Flatten groups → [header, ...its items, header, ...] for the virtualized list.
   const flatRows = useMemo<LibRow[]>(() => {
     const rows: LibRow[] = []
     for (const g of groups) {
       rows.push({ kind: 'header', title: g.title, items: g.items })
-      for (const it of g.items) rows.push({ kind: 'item', item: it })
+      if (groups.length === 1 || expandedGroups.has(g.title)) {
+        for (const it of g.items) rows.push({ kind: 'item', item: it })
+      }
     }
     return rows
-  }, [groups])
+  }, [groups, expandedGroups])
 
   const effStatus = (it: MediaItem): ItemStatus =>
     statusByUrl.get(it.url) ?? (it.downloaded ? 'completed' : 'pending')
@@ -335,6 +348,15 @@ export function LibraryView(): React.JSX.Element {
     })
   }
 
+  function toggleGroupExpand(title: string): void {
+    setExpandedGroups((prev) => {
+      const next = new Set(prev)
+      if (next.has(title)) next.delete(title)
+      else next.add(title)
+      return next
+    })
+  }
+
   function toggleGroup(groupItems: MediaItem[], on: boolean): void {
     setSelected((prev) => {
       const next = new Set(prev)
@@ -366,6 +388,16 @@ export function LibraryView(): React.JSX.Element {
     setBatchNote(`Queued ${n} download${n === 1 ? '' : 's'}.`)
   }
 
+  // Queue every actionable (pending/failed/canceled) video in one playlist group,
+  // so "download this whole playlist" is a single click.
+  function downloadGroup(groupItems: MediaItem[]): void {
+    if (!selectedSourceId) return
+    const toQueue = groupItems.filter(actionable)
+    if (toQueue.length === 0) return
+    const n = enqueueItems(selectedSourceId, toQueue)
+    setBatchNote(`Queued ${n} download${n === 1 ? '' : 's'}.`)
+  }
+
   function pillClass(status: ItemStatus): string {
     if (status === 'downloading' || status === 'queued') return mergeClasses(styles.pill, styles.pillDownloading)
     if (status === 'completed') return mergeClasses(styles.pill, styles.pillCompleted)
@@ -382,14 +414,45 @@ export function LibraryView(): React.JSX.Element {
   function renderRow(row: LibRow): React.JSX.Element {
     if (row.kind === 'header') {
       const allOn = row.items.every((it) => selected.has(it.id))
+      const open = isGroupOpen(row.title)
+      const groupActionable = row.items.filter(actionable).length
       return (
-        <div className={styles.groupHead}>
+        <div
+          className={styles.groupHead}
+          onClick={() => toggleGroupExpand(row.title)}
+          role="button"
+          tabIndex={0}
+          onKeyDown={(e) =>
+            (e.key === 'Enter' || e.key === ' ') && toggleGroupExpand(row.title)
+          }
+          aria-expanded={open}
+        >
+          {open ? <ChevronDownRegular /> : <ChevronRightRegular />}
           <AppsListRegular />
           <span className={styles.groupTitle}>{row.title}</span>
           <Caption1 className={styles.srcSub}>{row.items.length}</Caption1>
-          <Button size="small" appearance="subtle" onClick={() => toggleGroup(row.items, !allOn)}>
+          <Button
+            size="small"
+            appearance="subtle"
+            onClick={(e) => {
+              e.stopPropagation()
+              toggleGroup(row.items, !allOn)
+            }}
+          >
             {allOn ? 'None' : 'All'}
           </Button>
+          <Button
+            size="small"
+            appearance="subtle"
+            icon={<ArrowDownloadRegular />}
+            disabled={groupActionable === 0}
+            onClick={(e) => {
+              e.stopPropagation()
+              downloadGroup(row.items)
+            }}
+          >
+            Download{groupActionable > 0 ? ` ${groupActionable}` : ''}
+          </Button>
         </div>
       )
     }