feat(matching): split wrongly merged versions with watch-state reattribution; anchor group keys on provider tags (#319)

* feat(matching): split wrongly merged versions, reattribute watch state, anchor group keys on provider tags

Wrong merges (two titles normalizing to the same title+year key) stacked
different films as fake "versions" of one item with no in-app repair, and
explicit {tmdb-…}/[imdb-…] folder tags could not prevent it because the
content-group key ignored provider IDs entirely. Merges also silently
orphaned all per-user watch state.

- Anchor group keys on structured provider tags: same tag always groups,
  different tags can never merge; untagged files keep title+year keys.
- media_identity_overrides: path-scoped (root/file) forced identities applied
  during group inference, so admin splits survive rescans.
- internal/catalog/reattribute: shared user-state mover — exact moves for
  file-linked rows, evidence-based user_watch_history classification via the
  playback session log, newest-wins progress conflicts; wired into
  rebindItemToExistingItem to stop merge orphaning (with S/E episode mapping).
- POST /admin/items/{id}/split (dry-run = full transaction + rollback, so
  previews are exact), POST /admin/items/{id}/merge, GET /admin/items/{id}/files.
- Web admin: Split Versions dialog (files by folder → candidate search →
  preview → split), Resolve link from ambiguous-roots diagnostics.

Part of #318

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* fix(reattribute): classify history before moving session log; cover managed downloads and series-scoped preferences

Review findings on #319, all reproduced against a migrated scratch database:

- moveFileSubset re-pointed playback_history_admin before the history
  evidence query ran, erasing exactly the evidence proving a profile's plays
  were all on moved files — their history stayed behind as ambiguous.
  History classification now runs first; the pre-fix code demonstrably fails
  TestRun_HistoryEvidenceClassification.
- Managed offline downloads (downloads.content_id/episode_id) were not
  remapped on split or merge, stranding rows on the old id. Now moved per
  file on splits and swept per id pair on merges/episode re-anchoring.
- Series merges left user_audio_preferences, user_subtitle_preferences,
  user_series_playback_preferences (series_id-keyed) and the denormalized
  user_home_item_dismissals.series_id behind. All four now move, mirroring
  the provider-merge remap.

All five reattribute DB tests now verified green against PostgreSQL, with
new coverage for managed downloads, subtitle preferences, and dismissal
series ids.

Part of #318

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

web/src/api/types.ts

@@ -2945,6 +2945,8 @@ export interface LibraryRoot {
   first_seen_at: string;
   last_seen_at: string;
   active_override?: LibraryRootOverride;
+  /** Catalog item this group matched to, when known. */
+  content_id?: string;
 }
 
 export interface LibraryRootsResponse {
@@ -4135,6 +4137,68 @@ export interface ItemMatchApplyRequest {
   library_id?: number;
 }
 
+// Split/merge (wrong version-grouping repair) types
+
+export interface ItemFile {
+  id: number;
+  library_id: number;
+  file_path: string;
+  observed_root_path: string;
+  season_number?: number;
+  episode_number?: number;
+}
+
+export interface ItemFilesResponse {
+  files: ItemFile[];
+}
+
+export type SplitHistoryMode = "evidence" | "keep" | "move_all";
+
+export interface ItemSplitTarget {
+  provider_ids?: Record<string, string>;
+  content_id?: string;
+  unmatched?: boolean;
+  title?: string;
+  year?: number;
+}
+
+export interface ItemSplitRequest {
+  file_ids: number[];
+  target: ItemSplitTarget;
+  history_mode?: SplitHistoryMode;
+  persist_override?: boolean;
+  dry_run?: boolean;
+}
+
+export interface ReattributionReport {
+  playback_session_log: number;
+  downloads: number;
+  progress_moved: number;
+  progress_conflicts: number;
+  history_moved: number;
+  history_stayed: number;
+  history_ambiguous: number;
+  intent_moved: number;
+  episode_pairs_moved: number;
+  ambiguous_history?: {
+    user_id: number;
+    profile_id: string;
+    watched_at: string;
+  }[];
+}
+
+export interface ItemSplitResponse {
+  dry_run: boolean;
+  source_content_id: string;
+  target_content_id: string;
+  target_created: boolean;
+  files_moved: number;
+  root_overrides: string[];
+  file_overrides: string[];
+  episode_pairs: number;
+  reattribution: ReattributionReport;
+}
+
 // Image selector types
 export interface RemoteImage {
   provider_id: string;