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>

src/WatchState/Dto/playback-report.dto.ts

@@ -0,0 +1,37 @@
+import { BadRequestException } from '@nestjs/common';
+
+export type PlaybackEvent = 'start' | 'tick' | 'pause' | 'stop' | 'end';
+
+const EVENTS: PlaybackEvent[] = ['start', 'tick', 'pause', 'stop', 'end'];
+
+/** a player's progress report, positions in seconds */
+export class PlaybackReport {
+  constructor(
+    readonly position: number,
+    readonly duration: number | null,
+    readonly event: PlaybackEvent,
+    readonly client: string | null,
+    /**
+     * when it happened (ms since epoch), only for reports sent late (offline,
+     * imported history); live reports leave it out and get the server's time
+     */
+    readonly at: number | null,
+  ) {}
+
+  static fromBody(body: Record<string, unknown>): PlaybackReport {
+    const position = Number(body?.position);
+    if (!Number.isFinite(position) || position < 0) {
+      throw new BadRequestException('position (seconds) is required');
+    }
+    const duration = Number(body.duration);
+    const at = Number(body.at);
+
+    return new PlaybackReport(
+      position,
+      Number.isFinite(duration) && duration > 0 ? duration : null,
+      EVENTS.find((event) => event === body.event) ?? 'tick',
+      typeof body.client === 'string' ? body.client.slice(0, 32) : null,
+      Number.isFinite(at) && at > 0 ? at : null,
+    );
+  }
+}