add shared watch state, continue watching and new main menu

- watch_state table: resume point, watched, play count, last played per file,
  shared by all clients (Kodi plugin, Android TV app)
- POST/GET /api/state/:fileId for players' progress reports (watched at 90% or
  on end; late resends carry `at` and lose to newer state)
- listings carry watch state (files: playcount, resume, lastplayed; shows and
  seasons: watched/total episodes), episodes sorted by season/episode
- all/continue: unfinished files and next episodes, latest activity first
- context menus: mark (un)watched for a file, season or show; hide from
  continue watching
- main menu: Continue watching, Movies, Shows, scans (Torr/LRT unlisted)
- DATA_ROOT env overrides /srv/data for local runs outside docker

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

migrations/1791786266498-CreateWatchStateTable.ts

@@ -0,0 +1,29 @@
+import { MigrationInterface, QueryRunner } from 'typeorm';
+
+export class CreateWatchStateTable1791786266498 implements MigrationInterface {
+  public async up(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(
+      `create table watch_state
+       (
+           file_id     INTEGER primary key,
+           position    REAL    default 0 not null,
+           duration    REAL,
+           watched     TINYINT default 0 not null,
+           play_count  INTEGER default 0 not null,
+           last_played INTEGER,
+           updated_at  INTEGER not null,
+           client      VARCHAR(32),
+           hidden      TINYINT default 0 not null
+       );`,
+    );
+
+    await queryRunner.query(
+      `create index watch_state_last_played
+          on watch_state (last_played);`,
+    );
+  }
+
+  public async down(queryRunner: QueryRunner): Promise<void> {
+    await queryRunner.query(`DROP TABLE watch_state`);
+  }
+}