refactor(playlist): G.70 — extract three lifecycle hooks (route + bulk-picker dismiss + DnD reorder) (#637)

Three-cut cluster pulling the last cluster of useEffect bodies + the
DnD-reorder visual feedback out of PlaylistDetail.tsx. 452 → 423 LOC
(−29).

usePlaylistRouteEffects — bundles two route-driven effects:
contextMenu reset (clears contextMenuSongId whenever playerStore's
context menu closes) and openEditMeta-from-route (consumes the
`openEditMeta` location.state flag, opens the meta modal, and
clears the flag with a navigate-replace so back-nav doesn't
re-trigger). Subscribes to playerStore directly.

useBulkPlPickerOutsideClick — the global mousedown listener that
closes the bulk-add-to-playlist picker when clicking outside the
picker wrapper. No-op when closed.

usePlaylistDnDReorder — owns dropTargetIdx state, the
container.addEventListener('psy-drop', …) wiring that calls
runPlaylistReorderDrop, and the handleRowMouseEnter
drag-over-visual helper. Subscribes to DragDropContext directly.

PlaylistDetail drops the direct runPlaylistReorderDrop import and
the contextMenuOpen store subscription — both now live in the hooks
that need them. Pure code move otherwise.

src/hooks/useBulkPlPickerOutsideClick.ts

@@ -0,0 +1,15 @@
+import React, { useEffect } from 'react';
+
+export function useBulkPlPickerOutsideClick(
+  showBulkPlPicker: boolean,
+  setShowBulkPlPicker: React.Dispatch<React.SetStateAction<boolean>>,
+): void {
+  useEffect(() => {
+    if (!showBulkPlPicker) return;
+    const handler = (e: MouseEvent) => {
+      if (!(e.target as HTMLElement).closest('.bulk-pl-picker-wrap')) setShowBulkPlPicker(false);
+    };
+    document.addEventListener('mousedown', handler);
+    return () => document.removeEventListener('mousedown', handler);
+  }, [showBulkPlPicker, setShowBulkPlPicker]);
+}