refactor(playlist): G.61 — extract helpers + CSV import + modal components (cluster) (#628)

Four-cut cluster on PlaylistDetail.tsx. 2274 → 1761 LOC (−513); the page
keeps every behaviour and stateful path, but the leaf helpers, the
Spotify CSV import workflow, and the two stand-alone modals each live
in their own files now.

playlistDetailHelpers — pure helpers: sanitizeFilename, formatDuration,
formatSize, totalDurationLabel, codecLabel, plus SMART_PREFIX with
isSmartPlaylistName / displayPlaylistName. No deps beyond
formatHumanHoursMinutes + SubsonicSong. Kept the duplicates that
already live in ContextMenu / Sidebar / Playlists in place — dedup is
a separate cut, not part of this code-move.

spotifyCsvImport — full Spotify CSV pipeline: HEADER_MAPPINGS,
normalizeHeader, findColumnField, parseArtists, extractFeaturedArtists,
parseSpotifyCsv, plus the SpotifyCsvTrack type re-exported for callers.
papaparse moves with it; PlaylistDetail no longer imports Papa
directly. Header strings keep the \uXXXX escapes so the diff is
byte-identical.

PlaylistEditModal — full edit-meta dialog (name / description / public
toggle / cover swap / cover remove / save spinner). Props match the
old inline component verbatim. Uses React + i18next + CachedImage +
the same lucide icons (Camera, Loader2, X) and SubsonicPlaylist type.

CsvImportReportModal — full import-result dialog (4- or 5-cell stat
grid, duplicate / not-found / network-error lists, download-report
button via Blob + URL.createObjectURL). Still rendered through
createPortal to document.body so the z-index-99999 overlay clears
playlist UI. Imports the SpotifyCsvTrack type from the new CSV module.

PlaylistDetail loses createPortal and Papa from its import list, picks
up two component imports (PlaylistEditModal, CsvImportReportModal), and
the three util imports (playlistDetailHelpers, spotifyCsvImport, the
type-only SpotifyCsvTrack). Pure code move otherwise — no behaviour
change.

src/utils/playlistDetailHelpers.ts

@@ -0,0 +1,45 @@
+import type { SubsonicSong } from '../api/subsonicTypes';
+import { formatHumanHoursMinutes } from './formatHumanDuration';
+
+export function sanitizeFilename(name: string): string {
+  return name
+    .replace(/[/\\?%*:|"<>]/g, '-')
+    .replace(/\.{2,}/g, '.')
+    .replace(/^[\s.]+|[\s.]+$/g, '')
+    .substring(0, 200) || 'download';
+}
+
+export function formatDuration(seconds: number): string {
+  const m = Math.floor(seconds / 60);
+  const s = seconds % 60;
+  return `${m}:${String(s).padStart(2, '0')}`;
+}
+
+export function formatSize(bytes?: number): string {
+  if (!bytes) return '';
+  return `${(bytes / 1024 / 1024).toFixed(1)} MB`;
+}
+
+export function totalDurationLabel(songs: SubsonicSong[]): string {
+  const total = songs.reduce((acc, s) => acc + (s.duration ?? 0), 0);
+  return formatHumanHoursMinutes(total);
+}
+
+export const SMART_PREFIX = 'psy-smart-';
+
+export function isSmartPlaylistName(name: string): boolean {
+  return (name ?? '').toLowerCase().startsWith(SMART_PREFIX);
+}
+
+export function displayPlaylistName(name: string): string {
+  const n = name ?? '';
+  if (isSmartPlaylistName(n)) return n.slice(SMART_PREFIX.length);
+  return n;
+}
+
+export function codecLabel(song: SubsonicSong, showBitrate: boolean): string {
+  const parts: string[] = [];
+  if (song.suffix) parts.push(song.suffix.toUpperCase());
+  if (showBitrate && song.bitRate) parts.push(`${song.bitRate} kbps`);
+  return parts.join(' · ');
+}