refactor(folder-browser): G.87 — extract column component + 3 hooks (cluster, multi-commit) (#654)

* refactor(folder-browser): G.87.1 — extract helpers + types

Move ColumnKind / NavPos / Column types + entryToAlbumIfPresent /
entryToTrack mappers + isFolderBrowserArrowKey /
folderBrowserHasKeyModifiers key-event helpers into
src/utils/folderBrowserHelpers.ts. Pure code move.

* refactor(folder-browser): G.87.2 — extract FolderBrowserColumn component

* refactor(folder-browser): G.87.3 — extract useFolderBrowserNowPlayingPath hook

* refactor(folder-browser): G.87.4 — extract useFolderBrowserScrolling hook

* refactor(folder-browser): G.87.5 — extract useFolderBrowserKeyboardNav hook

src/utils/folderBrowserHelpers.ts

@@ -0,0 +1,85 @@
+import type React from 'react';
+import type { SubsonicAlbum, SubsonicDirectoryEntry } from '../api/subsonicTypes';
+import type { Track } from '../store/playerStoreTypes';
+
+export type ColumnKind = 'roots' | 'indexes' | 'directory';
+export type NavPos = { colIndex: number; rowIndex: number };
+
+export type Column = {
+  id: string;
+  name: string;
+  items: SubsonicDirectoryEntry[];
+  selectedId: string | null;
+  loading: boolean;
+  error: boolean;
+  kind: ColumnKind;
+};
+
+/** getMusicDirectory: `albumId` or `album` + row `id` (Navidrome). */
+export function entryToAlbumIfPresent(item: SubsonicDirectoryEntry): SubsonicAlbum | null {
+  if (!item.isDir) return null;
+  const albumId = item.albumId ?? (item.album ? item.id : undefined);
+  if (!albumId) return null;
+  return {
+    id: albumId,
+    name: item.album ?? item.title,
+    artist: item.artist ?? '',
+    artistId: item.artistId ?? '',
+    coverArt: item.coverArt,
+    year: item.year,
+    genre: item.genre,
+    starred: item.starred,
+    userRating: item.userRating,
+    songCount: 0,
+    duration: 0,
+  };
+}
+
+export function entryToTrack(e: SubsonicDirectoryEntry): Track {
+  return {
+    id: e.id,
+    title: e.title,
+    artist: e.artist ?? '',
+    album: e.album ?? '',
+    albumId: e.albumId ?? '',
+    artistId: e.artistId,
+    coverArt: e.coverArt,
+    duration: e.duration ?? 0,
+    track: e.track,
+    year: e.year,
+    bitRate: e.bitRate,
+    suffix: e.suffix,
+    genre: e.genre,
+    starred: e.starred,
+    userRating: e.userRating,
+  };
+}
+
+export function isFolderBrowserArrowKey(e: React.KeyboardEvent): boolean {
+  return (
+    e.key === 'ArrowUp' ||
+    e.key === 'ArrowDown' ||
+    e.key === 'ArrowLeft' ||
+    e.key === 'ArrowRight' ||
+    e.code === 'ArrowUp' ||
+    e.code === 'ArrowDown' ||
+    e.code === 'ArrowLeft' ||
+    e.code === 'ArrowRight'
+  );
+}
+
+/** Modifiers from native event + getModifierState (WebKit/WebView can miss flags on the synthetic event). */
+export function folderBrowserHasKeyModifiers(e: React.KeyboardEvent): boolean {
+  const n = e.nativeEvent;
+  if (n.ctrlKey || n.altKey || n.shiftKey || n.metaKey) return true;
+  if (typeof n.getModifierState === 'function') {
+    return (
+      n.getModifierState('Control') ||
+      n.getModifierState('Alt') ||
+      n.getModifierState('Shift') ||
+      n.getModifierState('Meta') ||
+      n.getModifierState('OS')
+    );
+  }
+  return false;
+}