Restructure step 4: local library and media identity

- L1 (core, offline): release names with kinds (episode, movie, extra:
  OP/ED/Opening/Ending/NC/PV/OVA…), folder hints (season and name from
  parentheticals, ranges), one show across folders, gaps and next with
  skipped numbers, junk ignored, stable keys.
- L2 (app, device-owned cache): AniList match with synonyms and
  sequel walking, episode mapping across cours (AnimeFlow runs when
  signed in), art and episode titles, "Wrong show?" pins per show or
  folder, episode offsets; lazy, spaced requests, works offline.
- Files tab as a library: poster cards, show pages with banner, gap
  prompt, extras, movies, Wrong show? and Episode numbers.
- media.ref produced for local files, Jellyfin (provider ids) and links,
  carried in swaps and Up next; receivers name media from it.
- Hosting relays each Jellyfin item through its own server's login.

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

apps/desktop/lib/src/files/scanner.dart

@@ -1,16 +1,13 @@
 import 'dart:io';
 import 'dart:isolate';
 
-import 'name_parser.dart';
+import 'package:sync_relay_core/core.dart';
 
-// Folder scan for the Files source: videos with their parsed names,
-// sidecar subtitles, everything else counted and hidden. The walk is
-// synchronous I/O, so it runs in its own isolate.
+export 'package:sync_relay_core/core.dart' show FileKind, LocalFile, kindOf, subtitleExtensions, videoExtensions;
 
-const videoExtensions = {
-  'mkv', 'mp4', 'webm', 'avi', 'mov', 'm4v', 'ts', 'm2ts', 'wmv', 'flv', //
-};
-const subtitleExtensions = {'ass', 'ssa', 'srt', 'vtt', 'sup'};
+// Folder scan for the Files source: the videos (grouped into shows by
+// core's `groupLocal`, L1), sidecar subtitles, everything else counted
+// and hidden. The walk is synchronous I/O, so it runs in its own isolate.
 
 /// Files looked at per scan; past this the result is [FolderScan.truncated].
 const maxScannedFiles = 20000;
@@ -18,27 +15,8 @@ const maxScannedFiles = 20000;
 /// Samples and trailers under this size are hidden next to the real thing.
 const _sampleMaxBytes = 300 << 20;
 
-enum FileKind { video, subtitle, other }
-
-FileKind kindOf(String path) {
-  final ext = _extension(_baseName(path));
-  if (videoExtensions.contains(ext)) return FileKind.video;
-  if (subtitleExtensions.contains(ext)) return FileKind.subtitle;
-  return FileKind.other;
-}
-
-class VideoFile {
-  final String path;
-  final int size;
-  final ParsedName parsed;
-  final DateTime modified;
-  const VideoFile(this.path, this.size, this.parsed, this.modified);
-
-  String get name => _baseName(path);
-}
-
 class FolderScan {
-  final List<VideoFile> videos;
+  final List<LocalFile> videos;
   /// Non-video files and samples (subtitles and dot-entries not counted).
   final int hiddenCount;
   /// Up to 6 of the hidden file names, for "and N other files" hints.
@@ -75,7 +53,7 @@ Future<FolderScan> scanFolder(String dir, {int maxFiles = maxScannedFiles}) =>
 
 /// The walk behind [scanFolder]; blocks, so call it from an isolate.
 FolderScan scanFolderSync(String dir, {int maxFiles = maxScannedFiles}) {
-  final videos = <VideoFile>[];
+  final videos = <LocalFile>[];
   final subs = <String>[];
   final examples = <String>[];
   var hidden = 0, seen = 0;
@@ -123,8 +101,7 @@ FolderScan scanFolderSync(String dir, {int maxFiles = maxScannedFiles}) {
         if (examples.length < 6) examples.add(name);
         continue;
       }
-      videos.add(VideoFile(e.path, size, parseReleaseName(name),
-          stat?.modified ?? DateTime.fromMillisecondsSinceEpoch(0)));
+      videos.add(LocalFile(e.path, size, stat?.modified ?? DateTime.fromMillisecondsSinceEpoch(0)));
     }
   }
   return FolderScan(
@@ -138,7 +115,7 @@ FolderScan scanFolderSync(String dir, {int maxFiles = maxScannedFiles}) {
 
 /// Subtitles in the same folder whose name is the video's base name,
 /// optionally followed by `.lang` / `.forced` style suffixes.
-Map<String, List<String>> _sidecars(List<VideoFile> videos, List<String> subs) {
+Map<String, List<String>> _sidecars(List<LocalFile> videos, List<String> subs) {
   final byStem = <String, List<String>>{};
   for (final s in subs) {
     final stem = _stripExtension(s);
@@ -163,93 +140,11 @@ Map<String, List<String>> _sidecars(List<VideoFile> videos, List<String> subs) {
   };
 }
 
-/// One show: its episodes in season/episode order plus its extras
-/// (NCOP, OVA...) in name order.
-class SeriesGroup {
-  /// Display title: the most common spelling among the files.
-  final String title;
-  final String key;
-  final List<VideoFile> episodes;
-  final List<VideoFile> extras;
-  const SeriesGroup(this.title, this.key, this.episodes, this.extras);
-
-  /// Distinct seasons, ascending; files without one count as season 1.
-  List<int> get seasons =>
-      ({for (final e in episodes) e.parsed.season ?? 1}.toList()..sort());
-}
-
-/// [groupBySeries] result: shows, and videos that are not episodes.
-class GroupedVideos {
-  final List<SeriesGroup> series;
-  final List<VideoFile> loose;
-  const GroupedVideos(this.series, this.loose);
-}
-
-/// Groups videos with an episode number (or an extra marker) by
-/// [ParsedName.seriesKey]; the rest (movies, clips) stay loose, by name.
-/// An extra whose series has no episodes in the list is loose too.
-GroupedVideos groupBySeries(Iterable<VideoFile> videos) {
-  final episodes = <String, List<VideoFile>>{};
-  final extras = <String, List<VideoFile>>{};
-  final loose = <VideoFile>[];
-  for (final v in videos) {
-    final p = v.parsed;
-    final key = p.seriesKey;
-    if (p.episode != null && key.isNotEmpty) {
-      episodes.putIfAbsent(key, () => []).add(v);
-    } else if (p.extra != null && key.isNotEmpty) {
-      extras.putIfAbsent(key, () => []).add(v);
-    } else {
-      loose.add(v);
-    }
-  }
-  for (final e in extras.entries) {
-    if (!episodes.containsKey(e.key)) loose.addAll(e.value);
-  }
-  int byName(VideoFile a, VideoFile b) =>
-      a.name.toLowerCase().compareTo(b.name.toLowerCase());
-  final groups = [
-    for (final e in episodes.entries)
-      SeriesGroup(
-        _commonTitle(e.value),
-        e.key,
-        e.value..sort(_byEpisode),
-        (extras[e.key] ?? [])..sort(byName),
-      ),
-  ]..sort((a, b) => a.title.toLowerCase().compareTo(b.title.toLowerCase()));
-  return GroupedVideos(groups, loose..sort(byName));
-}
-
-int _byEpisode(VideoFile a, VideoFile b) {
-  final pa = a.parsed, pb = b.parsed;
-  final s = (pa.season ?? 1).compareTo(pb.season ?? 1);
-  if (s != 0) return s;
-  final e = pa.episode!.compareTo(pb.episode!);
-  if (e != 0) return e;
-  // Same episode twice (v2, another group): newest release first.
-  return b.name.compareTo(a.name);
-}
-
-String _commonTitle(List<VideoFile> files) {
-  final counts = <String, int>{};
-  for (final f in files) {
-    counts.update(f.parsed.series, (n) => n + 1, ifAbsent: () => 1);
-  }
-  return counts.entries
-      .reduce((a, b) => b.value > a.value ? b : a)
-      .key;
-}
-
 String _baseName(String path) {
   final i = path.lastIndexOf(RegExp(r'[/\\]'));
   return i < 0 ? path : path.substring(i + 1);
 }
 
-String _extension(String name) {
-  final dot = name.lastIndexOf('.');
-  return dot <= 0 ? '' : name.substring(dot + 1).toLowerCase();
-}
-
 String _stripExtension(String path) {
   final dot = path.lastIndexOf('.');
   final sep = path.lastIndexOf(RegExp(r'[/\\]'));